We studied the effects of LHRH and its analogs on plasminogen activator production and progesterone and estradiol secretion by granulosa cells isolated from adult rat Graafian follicles. LHRH and its agonist ([des- -Gly10,D-Trp6,Pro9-NHEt]LHRH) stimulated small but significant increases in plasminogen activator production. This stimulatory action of LHRH was blocked by the addition of the specific antagonist ([D- pGlu1,D-Phe2,D-Trp3,6]LHRH). In contrast, LHRH treatment had no significant effect on basal steroid production by granulosa cells of Graafian follicles cultured for 2-6 days. However, LHRH decreased the FSH-stimulated steroidogenesis. This inhibitory effect of LHRH on steroidogenesis was abolished by concomitant addition of the LHRH antagonist. The results show that LHRH has a stimulatory effect on plasminogen activator production and a suppressive action on steroidogenesis in granulosa cells isolated from Graafian follicles of adult rats.