Heat shock has a profound influence on the metabolism and behavior of eukaryotic cells. We have examined the effects of heat shock on the release from cells of arachidonic acid and its bioactive eicosanoid metabolites, the prostaglandins and leukotrienes. Heat shock (42-45") increased the rate of arachidonic acid release from human, rat, murine, and hamster cells. Arachidonate accumulation appeared to be due, at least partially, to stimulation of a phospholipase AL activity by heat shock and was accompanied by the accumulation of lysophosphatidylinosilol and lysophosphdlidylcholitie in membranes. Induction of arachidonate release by heat did not appear to be mediated by an increase in cell Ca++. stimulation oi arachidonate release by heat shock in hamster fibroblasts was quantitatively similar to the receplor-mediated effects of c1 thrombin and bradykinin. The effects of heat shock and a thrombin on arachidonate release were inhibited by glucocorticoids. Increased arachidonate release in heat-shocked cells was accompanied by the accelerated accumulation of cyclooxygenase products prostaglandin EL and prostaglandin FZct and by 5-Iipoxygenase metabolite leukotriene B4. Elevated concentrations of arachidonic acid and metabolites may he involved in the cytotoxic effects of hyperthermia, in homeostatic responses to heat shock, and in vascular and inflammatory reactions to stress.