Rat liver plasma membranes were isolated from rats intoxicated acutely and chronically with carbon tetrachloride and a quantitative analysis of lipids was performed. Membranes from regenerating liver (acute intoxication) are characterized by a 60% drop in total phospholipids with a diminished phosphatidylcholine/phosphatidylethanolamine ratio (PC/PE) and a markedly decreased cholesterol level during the first 3 days after the intoxication, leading to a drastically decreased cholesterol/phospholipid (PL) ratio. In the chronically intoxicated rats (non-regenerating liver), although the phospholipids are diminished, phosphatidylcholine and phosphatidylethanolamine are equally decreased, and therefore the PC/PE ratio is not changed. Cholesterol is not diminished and, since the phospholipids are very low, the ratio cholesterol/PL is increased. These data could be correlated with the membrane fluidity. A decrease in the cholesterol/PL ratio results in a more fluid lipid matrix in the proliferative state of the cell. Treatment with colchicine during chronic intoxication prevented the increase in the cholesterol/PL ratio and improved the clinical conditions of the rats. The modulation of the cholesterol content could be a mechanism to control membrane fluidity during the different physiological states of the cell.