AbstractThe effect of exposure to chlorinated insecticides (DDT and toxaphene) on Na+, K+‐ATPase, Mg2+‐ATPase and Ca2+‐ATPase activities of the plasma membrane of hepatocytes was determined. Acute treatment with DDT (200 mg per kg body weight) or toxaphene (110 mg per kg body weight) produced a significant decrease in Na+, K+‐ATPase activity (80% and 85%, respectively) 24 h after treatment. DDT also produced a 30% decrease in Mg2+‐ATPase and Ca2+‐ATPase activity, but toxaphene treatment did not modify these enzymes. The effect of exposure to daily doses of DDT (30 mg per kg body weight) or toxaphene (16.5 mg per kg body weight) for a period of 3.5 months was also studied. Animals were sacrificed at 15‐day intervals and results showed that Na+, K+‐ATPase activity decreased 80% from the beginning of each treatment and the activity remained low throughout the treatment period. DDT, but not toxaphene, also led to a decrease in Mg2+‐ATPase (20%) and Ca2+‐ATPase (35%) activity. The low values observed from the beginning remained low throughout the treatment period. We believe that the general mechanism of ATPase inhibition by organochloride compounds could be the result of its interaction with membrane lipid components, although some differences could arise from differences in thei