In order to elucidate the putative role of inhibin in regulation of spermatogenesis, expression of inhibin subunits was examined at defined stages of the cycle of the rat seminiferous epithelium. Twenty 2-mm segments of seminiferous tubules at stages XIII-I, II-VI, VII-VIII, and IX-XII were dissected using the transillumination technique and subunit specific messenger RNAs (mRNAs) were quantitated by filter hybridization. The alpha and beta-B subunit mRNAs varied significantly in different stages, the highest levels of both alpha and beta-B subunit expression were seen in stages XIII-I and the lowest in stages VII-VIII. The hybridization signals obtained with beta-actin probe were not significantly different between different stages indicating that the differences in the quantities of subunit mRNAs in different stages were not due to different amounts of RNA blotted. beta-A subunit mRNA levels were below the detection limit of the filter hybridization method. These data demonstrate that expression of inhibin alpha and beta-B subunits in the rat testis is stage dependent and suggest a paracrine role for inhibin-related peptides in regulation of spermatogenesis.