We have demonstrated for the first time that (i) mouse Sertoli cells predominantly secrete tPA under the action of FSH and cAMP-generating agents, whereas Leydig cells mainly produce uPA; (ii) Sertoli cells are also capable of secreting PAI-1, as well as FSH, growth factors and GnRH increase PAI-1 gene expression; (iii) the increases in tPA and PAI-1 activities by different hormones in the conditioned media of Sertoli cells correspond to the increases in the levels of tPA and PAI-1 mRNA in the cultured cells, suggesting that the synthesis of the activator-inhibitor in mouse Sertoli cells is regulated at a transcriptional level and the tPA secreted by Sertoli cells may be involved in the spermatogenesis.