The effect of human membrane-associated phospholipase A2 (M-PLA2) on DNA synthesis in fibroblasts was examined in order to clarify its biological function. Human M-PLA2 added exogenously to the fibroblast cell lines Swiss 3T3 and BALB/3T3 was found to augment their DNA synthesis. This stimulation of DNA synthesis was not affected by treatment with indomethacin. Our results suggest that human M-PLA2 itself has a mitogenic effect on fibroblasts independent of arachidonate products such as prostaglandins.