The expression and localization of mRNA's for tissue plasminogen activator (tPA), urokinase PA (uPA), uPA receptor (uPAR) and inhibin subunits, alpha, beta A and beta B in monkey testes was investigated. Using in-situ hybridization with digoxigenin-labelled cRNA probes (dig-cRNA), we demonstrated that tPA and plasminogen activator inhibitor type 1 (PAI-1) were expressed in testes of both immature and mature rhesus monkeys. tPA mRNA was localized predominantly in Sertoli cells. Expression level was low in immature testis, increased dramatically in the adult and varied with seminiferous cycle. PAI-1 mRNA was localized mainly in germ cells except late spermatids. uPA mRNA was expressed stage-specifically in Sertoli cells of adult testis. uPA receptor mRNA was localized in germ cells of mature testis but not in spermatogonia or late spermatids. Assayed by fibrin overlay technique, PA activity in conditioned media of purified Sertoli cells (Sc) was negligible, PA activity in media obtained from co-cultured Sertoli and Leydig cells (LS), however, was significantly increased, although Leydig cells alone were not capable of producing any PA activity. Addition of follicle stimulating hormone (FSH) to the incubation medium remarkably increased PA secretion in both Sc and LS cultures. Human chronic gonadotrophin (HCG) had no significant effect on PA activity in the Sc culture but dramatically stimulated PA activity in the co-culture system. Dihydrotestosterone (DHT) did not mimic the effect of HCG. PAI-1 activity was secreted mainly by germ cells and did not differ between the two culture systems. FSH and forskolin inhibited PAI-1 secretion. Inhibin alpha, beta A and beta B subunit mRNAs were localized in Sertoli cells of adult monkey testes, with no obvious difference in the expression levels. These data suggest that PA/PAI-1 and other related factors are expressed in rhesus monkey testis under the control of various hormones, seminiferous cycle and cell-cell interactions through paracrine or autocrine regulation. Locally generated fibrinolysis may play an important role in the process of spermatogenesis.