Hybridization histochemistry has been used to detect the presence of mRNA for the α and β(A) subunit of inhibin in tissue sections of the ovary of cows. 32P-labelled cDNAs, complementary to the bovine α or β(A) subunit of inhibin or to a control segment of plasmid DNA (pBR 322), were used. The α subunit mRNA was located in the granulosa layer of antral follicles > 10.3 mm in diameter while the α and β(A) subunit mRNA were both present in follicles of > 0.8 mm. In these latter follicles, the thecal layer hybridized with only the α subunit mRNA. No hybridization of the α or β(A) subunit probe was found in the cells of the corpus luteum. Hybridization of both probes was abolished when the tissue sections were pretreated with ribonuclease (RNAse). The plasmid cDNA did not hybridize to any of the tissue sections. This study demonstrates that mRNA for the α inhibin subunit can be detected in granulosa and theca cells whereas the β(A) inhibin subunit mRNA is restricted to the granulosa cells. These results provide evidence for an independent regulation of expression for the two subunits of inhibin.