After having demonstrated the impairment of the microsomal oxidation process in rats treated with toxic Spanish cooking oil or fatty acid anilides, we studied the possibility that the function of the cytoplasmic membrane had been affected. For this, the activities of glucose-6-phosphatase and adenosintriphosphatase were determined, these being enzymes of utmost importance in transport at the liver cell membrane level. Wistar rats received disease-related toxic rapeseed oil (1 mg/kg/day) or linoleilanilide (50 mg/kg/day) for 6 days, and the animals were sacrificed immediately after the administration period and after a 4-, 8- and 12-week latency period. Enzyme activities were measured in the membrane fraction of liver and lung. The results showed considerable reduction (up to 80%) in the activity of these enzymes, confirming that transport mechanisms through cell membranes must have been impaired.