The effect of exogenous phosphatidylcholine on structure and function of plasma membranes from HIV-1-producing cells and from their non-infected counterparts was determined. The membrane protein composition was not affected by phospholipid treatment. Membrane fluidity and Ca 2+-permeability were increased in virus-producing cells and in control cells after lipid treatment. The triacylglycerol content of the plasma membranes was increased in virus-producing cells after lipid treatment, whereas the content of phospholipid and cholesterol was not changed. The increased triacylglycerol content was in accordance with a relatively higher rate of [ 14C]oleic acid incorporation into triacylglycerols of the virus-producing cells after lipid treatment as shown by metabolic labeling. The results suggest that a latent cytopathic effect of HIV-infection becomes manifest if the cells are exposed to exogenous phospholipid and this may open a way to preferentially eliminate HIV-producing cells.