The role of Zn(II) on the folding of bovine carbonic anhydrase B has been investigated by various physicochemical methods in order to understand how metal ions participate in the folding of metalloenzymes. Comparative studies of the native holoenzyme, the apoenzyme and the regenerated holoenzyme suggest no significant conformational differences. However, removal of zinc from the native holoenzyme decreases its conformational stability toward denaturation by acid and by guanidine hydrochloride. A biphasic profile was observed in guanidine hydrochloride denaturation of the apoenzyme instead of a single step transition observed with the holoenzyme. Moreover, the refolding of the random coiled polypeptide in the absence of zinc proceeds at a much slower rate than the folding with zinc. The role of zinc appears to stabilize part of the molecule and enable the whole protein to act as a more cooperative unit. It increases the rate of folding, but does not appear to be a necessary part of the information required for the folding process.