Treatment of GH3 cells for 24-72 h with sodium valerate (1 mM) increased 2- to 4-fold the production of both PRL and GH. There was a concomitant change in the morphology of the cells that resembled that produced by TRH and epidermal growth factor. The increases in hormone production and changes in morphology were reversible. The sodium salts of butyric, hexanoic, caprylic, nonanoic, and dodecanoic acids also increased hormone production and altered cell morphology, whereas the salts of formic, acetic, and isobutyric acids did not. Acute (1-h) treatment with the fatty acids, unlike the effects of TRH and epidermal growth factor, did not increase the release of PRL from the cells.