Follicular fluid was collected from individual human ovarian follicles and its effects, alone or in combination with frog pituitary homogenate (FPH), on oocyte maturation and ovulation were assessed following incubation with amphibian ovarian follicles in vitro. Oocyte maturation, with little or no concomitant ovulation, was induced by variable amounts of follicular fluid. Some of the individual follicular fluid samples were very active in inducing oocyte maturation, whereas others were inactive. Frog pituitary homogenates exhibited biologic activity (induced oocyte maturation and ovulation) when incubated in the presence of most follicular fluid samples. However, follicular fluid samples from two individuals inhibited ovulation but not maturation in FPH-treated follicles. These results demonstrate that amphibian follicles remain viable and undergo a number of physiologic changes in the presence of unfractionated human follicular fluid. Under appropriate conditions both stimulatory and inhibitory effects of follicular fluid were observed. These data suggest that amphibian ovarian follicles may provide a simple and independent means for detecting and assaying a number of biologic activities present in follicular fluid obtained from single human and other mammalian ovarian follicles. Such results may provide the basis for dissociating endocrine and cellular interactions which occur during normal and abnormal follicular differentiation.