Inhibins and activins are members of the transforming growth factor beta (TGF beta) superfamily. Since TGF beta has been shown to be a potent proliferation-inhibiting agent for the pituitary adenocarcinoma cell line, GH3, we determined whether this cell line (a) transcribes mRNAs coding for inhibin/activin subunits (alpha and beta A) and activin receptors I, II, and IIB; and (b) produces inhibin and/or activin proteins. Messenger RNAs for the alpha- and beta A-subunits of inhibin and activin receptors I, II, and IIB in GH3 cells were detected and localized using the reverse transcription-polymerase chain reaction (RT-PCR) analysis and in situ hybridization, respectively. The identity of the RT-PCR products was confirmed by DNA sequencing of PCR products. Immunocytochemically, inhibin and activin were localized in these cells. Our findings indicate that messenger RNAs encoding inhibin alpha- and beta A-subunits and activin receptors I, II, and IIB were expressed, and inhibin/activin proteins were produced, by GH3 cells, imply that these gonadal growth factors may have paracrine/autocrine functions in rat pituitary adenocarcinoma. Further, these observation suggest that these growth factors may be involved in regulating the growth and differentiational of rat pituitary adenocarcinoma cells.