In this study, the protein and mRNA expression of the short and long forms of Prolactin (PRL) receptors (PRL-R) were examined by means of Northern and Western blotting analyses in rat testicular Sertoli cells. Transcripts for the short and long forms of PRL-R were detected with specific probes, five major mRNA species of about 1.9, 2.6, 3.0, 3.7 and 5 kb for the short form and two of about 10 and 1.3 kb for the long form. Under reducing conditions, the use of a specific antibody for the short form revealed a major molecular species of approximately 45 kDa. Two groups of molecular species were detected for the long form, several bands with high molecular masses (110-300 kDa) and others about 45-60 kDa. Finally, the expression of the long form of PRL-R was shown to be hormonally regulated as it was inhibited by follicle stimulating hormone (FSH) (ED50 = 5 ng/ml). Together, the localisation of PRL receptors to Sertoli cells as well as the regulatory action of FSH on these receptors suggest that PRL and or (a) PRL-like activity(ies) might be considered as (a) potential regulator(s) of spermatogenesis.