The denaturation of chorionic gonadotropin in 40 per cent aqueous urea solution has been found exceptional with respect to both the heat of activation and entropy of activation, but similar to other protein denaturations when compared on the basis of free energy of activation (1). The low rate (2) of inactivation of mare serum gonadotropin in 40 per cent aqueous urea solution at 37.5”, along wi...