An embryo-derived platelet activating factor has been demonstrated to play an important role in reproduction. This report examined the effect of various doses of a synthetic platelet activating factor on the production of progesterone by porcine granulosa cells in culture. Granulosa cells aspirated from ovarian follicles of prepubertal gilts were grown for 24 hours in Dulbecco's Modified Eagles Media: Ham's F-12 with 5% fetal bovine serum and 1 micrograms/ml insulin. Cells were washed once in serum-free media and then cultured for an additional 48 hours with 0 to 5000 ng/ml of the platelet activating factor in media containing either 0.25% bovine serum albumin or 1% fetal bovine serum. Cells grown with fetal bovine serum produced 50% of the amount of progesterone that was produced in the absence of serum. Low doses of the platelet activating factor caused a slight decrease in progesterone production. Higher doses (greater than 500 ng/ml) in serum-free media caused a marked decrease in progesterone production. Serum had a protective effect at high doses of platelet activating factor which was probably mediated by enzymatic degradation of the platelet activating factor. In summary, platelet activating factor had no stimulatory effect on production of progesterone by porcine granulosa cells in culture.