Previous studies have shown an increase in the intracellular free arachidonic acid content associated with a disturbance in phospholipid metabolism in P815 tumor cells exposed to subtoxic concentration of tert-butyl hydroperoxide. The present study was to determine the respective contribution of the major phospholipid-metabolizing enzymes that could be involved in this process. The enzymes (phospholipase A, lysophospholipase, acylCoA:lysophosphatidylcholine acyltransferase and acylCoA synthetase) were studied under their respective optimal conditions. When P815 cells were treated with 50 microM of tert-butyl hydroperoxide, a significant stimulation (x 2.5) of phospholipase A was observed after 15 min of treatment. The activity of the acyltranferase tended to be higher in cells treated by tert-butyl hydroperoxide while the other enzyme activities (lysophospholipase and acyl CoA synthetase) were not affected. t-BHP did not significantly induce higher levels of lipid peroxides in P815 cells. These results show that, in the tumor cell line P815, the disturbance of phospholipid and arachidonate metabolism induced by t-BHP is linked to phospholipase A, the activation of which seems independent of oxidative stress.