Using differential heat capacity calorimetry, four structural transitions can be observed for the human erythrocyte ghost. These are centered at 50 degrees (A), 57 degrees (B), 63 degrees (C), and 77 degrees (D) when the suspending buffer is 77 imosm phosphate, pH 7.4. These transitions have been shown to be associated with the denaturation of membrane-bound proteins. Studies @re now being carried out which will provide information as to which specific proteins of the membrane participate in each of these transitions. The denaturation and renaturation of ribonuclease has been shown to be kinetically complex- consisting of a fast and a slow step. It is also known that different structural forms of active ribonuclease can be formed either by reoxidation of the reduced protein or by heat treatment of native ribonuclease. By studying the kinetics of folding and refolding of these structural variants, it is hoped to ascertain whether heterogeneity of the native protein is related to the complexities in the kinetics of folding and unfolding.