I saw this opening in a game recently and I want to know how to combat it. The intent of the Bishop move is that if NxN the Bishop recaptures and the centre is under no pressure while if the Knight doesn't take it has to retreat to either b6, where it prevents Black from using his c pawn, or f6 where it blocks the Bishop. Help!

Not sure if I've ever faced this continuation, but it doesn't strike me as particularly strong.  Ok, the bishop will end up on c3 where it opposes the Bg7, noted... but that's one less defender that White can bring to the d-pawn, since he won't be recapturing bxc3.  I don't think I'd play it any differently -- I'd still exchange on c3 after e4, and attack the center in the same way with Bg7/c5/Nc6.

I think the Bc3 is more dangerous than that because the d pawn is not pinned: after .d5 BxB bxB Black doesn't have his fianchetto

I looked it up in Game Explorer, and I guess the Bd2 continuation isn't that rare; there are hundreds of games like that.  White does score pretty well; the most common continuation from your final position is Bg7 e4 Nb6.

Is that GM or all games?

5 Bd2 actually scores better than  5 e4 !  Another strange move is  5 Na4 !? and it scores the same as 5 e4 ....... strange isnt it ?

There aren't many (if any) GM games in the Game Explorer, from what I can tell -- I usually search on the "Master Games" option.

I did compare the position against my database of 100k GM games, and e4 is still the better continuation there.  In that database, 5.e4 scores +312=438-176 (57.3%), and 5.Bd2 scores +22=43-18 (52.4%).  I don't totally trust the numbers of offbeat variations in Game Explorer for that type of reason... I think lower-level masters get caught off guard OTB by unusual continuations and don't always respond accurately.

For your perusal, here are a couple of sample games where Black won against Bd2.  The GMs seem to almost always play Nb6 against it:

Korchnoi v. Kasparov: http://www.chessgames.com/perl/chessgame?gid=1005678

Korchnoi v. Spassky: http://www.chessgames.com/perl/chessgame?gid=1405704

Vallejo-Pons v. Svidler: http://www.chessgames.com/perl/chessgame?gid=1395908

Nice topic, BTW, always good when I can learn something!

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I wouldn't care too much about those scores.
5.Bd2 looks very strange to me - this bishop is much better placed on e3!

I agree that the bishop would be good on c3, but as the sample games posted by Spiffe indicate, I think black has no problems after Nb6...

5.Bd2 is somewhat more passive than 5.e4!. The center will not be as strong and piece play will be the major factor later in the game. The idea behind the Exchange Grunfeld is for White to build up a big center, so this sideline move doesn't strike me as particularily effective.

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 After Nb6 the bishop does go to e3 and white has discouraged black from exchanging minor pieces on c3. I think this line is fine for white if he does some preparation.

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 Its always nice to have a C class player explain what the gruenfeld ideas are to keep me in my place. 

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True that there's nothing wrong with the line for white. But compared to the "normal" exchange variation followed by Bc4, Ne2 I think the Bd2 line is posing fewer problems for black.
In that perspective, I consider 5.Bd2 to be inferior.

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 And you are basing this on what? Your feelings ? I checked chess assistant with over 2 million games total and 5 Bd2 scores 59% for white while the line you mention scores 53%. How is that "inferior" ?

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I admit that I based my statement on feelings. The Bc4, Ne2 setup is critical for black. This is a fact - based on thousands of master games throughthe last 20 years or so...

The 5.Bd2 may score better for white. But this is most likely due to

a) significantly fewer games in the database
b) surprise factor. This is not a move that black Grunfeld players would normally expect

Objectively I believe black is perfectly ok after 5.Bd2 Bg7 6.e4 Nb6 (or even 6...Nxc3 which has been played quite a few times recently)

I certainly agree that the exchange variation is critical in the gruenfeld, both the line you mention with Bc4 & Ne2 set up as well as the more modern Nf3 & Be2 set up with usually 8 Rb1. A gruenfeld devotee has plenty of work to do just in those two lines alone and then there is also the Russian system and the "quiet" line that Petrosian crushed Fischer with in their 1971 candidates match 4 . Bf4 .

Heh, keep in mind there's quite a bit of sampling bias in my selected games -- I deliberately posted games where Black wins, to give some illustrations to a fellow Grunfeld player about how to approach this variation.  Don't take that to mean that Black "has no problems" based on that, because there are plenty of White wins available as well.  I guess my database disagrees with Reb's about whether Bd2 or e4 scores better, but either way they both score pretty well.

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 What does your data base say? You use chessbase? I have chess assistant.

I use ChessDB, actually, because I was too cheap to buy a commercial one.   The games database itself, I don't recall where I got it, but it seems to be all games where both players were over ELO 2500 or so -- post-WWII grandmaster play, 100k games worth.  The stats were quoted in an earlier post: 5.e4 scores +312=438-176 (57.3%), and 5.Bd2 scores +22=43-18 (52.4%).

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Using Chessbase and a reference database of almost 7 million games (MegaDB, UltraCorr + ICC/Playchess/Misc games) I found the following:

27933 games total

e4 = 54.2% in 24762 games.

Bd2 = 59.9% in 1278 games.  Highest rated players who have used this sideline Topalov, Kramnik, Radjabov and Morozevich.

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 Thanks Gonnosuke. I think of the not so popular choices at move 5 for white it must be as good as any. Chess Assistant also gives it scoring about 5% better than 5 e4 but from a base of only about 2 million games. In any event I have decided I am gonna try it myself some against some of the gruenfeld players here in Portugal to see how I fare with it. I am surprised to see Kramnik among the players who have played it, to be honest.