Rat liver inner mitochondrial membranes, were subjected to the solubilizing action of the non-ionic detergent Triton X-100 under a variety of ionic strength and temperature conditions. Increasing ionic strength has little influence on the amount of solubilized membrane protein and lipid phosphorus. CaCl increases the proportion of solubiized protein. This effect is preserved by 1 mM EDTA. Increasing temperatures decrease the proportion of protein solubilized by the detergent. SDS[sodium dodecyl suflate]polyacrylamide gel electrophoresis reveals no difference in polypeptide composition of the membrane fraction solubilized under the various conditions. Differences are observed in the solubilization of individual cytochormes. The data are interpreted in terms of changes in membrane architecture induced by the various conditions of the incubation medium.