Release of the organic osmolyte taurine efflux from NIH3T3 cells is increased by osmotic cell swelling in hypotonic medium and decreased by osmotic cell shrinkage in hypertonic medium. Release of arachidonic acid is increased under hypotonic conditions if oxidation of the fatty acid via the 5-lipoxygenase (5-LO) system is prevented by the 5-LO inhibitor ETH 615-139 and is reduced under hypertonic conditions. Exposure to the amphiphilic bee venom peptide melittin, which has no effect on the kinetic properties of PLA2 but promotes substrate replenishment, induces release of arachidonic acid and taurine in NIH3T3 cells under isotonic conditions. The potentiating effect of melittin on arachidonic release and taurine efflux is substantially increased in osmotically swollen cells and almost abolished in osmotic shrunken cells. H2O2 potentiates the melittin-induced taurine efflux under isotonic conditions but has only a minor effect on the melittin-induced taurine efflux under hypertonic conditions. Bromoenol lactone and manoalide, known inhibitors of Ca2+-independent phospholipase A2 (iPLA2) and secretory phospholipase A2 (sPLA2), respectively, reduce arachidonic acid and taurine release from NIH3T3 cells under hypotonic conditions and following addition of melittin. It is suggested that iPLA2/sPLA2 activity is responsible for the volume-sensitivity of taurine release in NIH3T3 mouse fibroblasts.