The ion permeability of human erythrocyte membrane displays two maxima at 48-52 degrees C and 62-67 degrees C [6, 8]. Both these independent maxima were investigated in modified membranes in order to elucidate the participation of the main types of membrane proteins. The modification protocols included the bilateral proteolytic digestion of membranes with 2-20 micrograms/ml trypsin, denaturation of the peripheral protein spectrin by exposing the membranes to 50 degrees C for 4 min or 1.5 M urea for 20 h, and preparation of the inside-out vesicles depleted of main peripheral proteins. Only the second maximum was registered in these membranes. Also, both maxima were absent in the unilamellar liposomes prepared from lipids extracted from intact membranes. The results indicate that different types of proteins were involved in the two disturbances: peripheral proteins (mainly spectrin)--in the first one and part of integral proteins-in the second. The different sensitivities of the disturbances to local anesthetics, protein thermostabilizers, n-alcohols, and detergents correlated with this conclusion. A correlation between the peak temperature of the second disturbance and the sphingomyelin content in the membrane of mammalian erythrocytes was also shown.