Circular dichroism (CD) of the hypocalcemic protein purified from bovine parotid gland was studied under various conditions. The CD spectra and hypocalcemic activity were measured after incubation of the sample in 6.6 M urea or 6 M guanidine hydrochloride (Gdn-HCl) and subsequent removal of the denaturants by dialysis. The sample dialyzed after incubation in 6.6 M urea retained the hypocalcemic activity and its CD spectra were very similar to that of the native protein. The sample treated in the same way with 6 M Gdn-HCl had no activity, though its CD pattern was similar to that of the native protein. The pattern of thermal transition at [θ]222 of the urea-treated sample resembled that of the native protein but that of the Gdn-HCl-treated sample was slightly different from that of the navive protein. The CD pattern of the sample reduced with mercaptoethanol showed a slightly low α-helix content and the hypocalcemic activity was also low compared to the native protein. Scission of the peptide bond was not found from the results of polyacrylamide gel disc electrophoresis of these samples.