We have used isolated rat hepatocytes to study whether the insulin-induced reduction of its own receptors may modify the transduction of hormone signals by changes in the content of a glycosyl-phosphatidylinositol. Both subsequent insulin binding and glycosyl-phosphatidylinositol concentrations markedly decreased as a function of time and insulin concentration during preincubation of hepatocytes with insulin. The modifications observed in insulin binding were due to changes in receptor concentration. These results show that insulin regulates both the number of its own receptors and glycosyl-phosphatidylinositol concentrations in target cells, which may be of interest in many pathophysiological situations.