Effects of transforming growth factor beta-1 (TGF-beta1) and all-trans-retinoic acid (All-trans-RA) on development of bulbourethral glands (BUGs) of neonatal mice were investigated in vitro. BUGs from 0-day-old male mice were cultured for 6 days in serum-free, chemically defined medium containing transferrin and bovine serum albumin, supplemented with 5alpha-dihydrotestosterone (DHT; 10-8 M) and insulin (10 microg/mL) alone or in combination. Prior to culture, BUGs from 0-day-old mice consisted of a simple epithelial rudiment encapsulated by mesenchyme. Epithelial growth and ductal branching occurred in BUGs cultured in medium containing DHT and insulin or DHT alone, but epithelial branching did not occur in BUGs cultured in the presence of insulin alone. Addition of TGF-beta1 at concentrations of > 5 ng/mL (0.2 x 10-9 M) to medium containing both insulin and DHT, inhibited the expected increase in overall size of BUGs, epithelial area and ductal branching in a dose-dependent manner. TGF-beta1 also decreased [3H]-thymidine labelling indices of both epithelium and mesenchyme. TGF-beta1 at 10 ng/mL elicited these inhibitory effects on BUGs cultured in medium containing DHT alone. Addition of All-trans-RA (10-8 to 10-6 M) to the medium containing DHT plus insulin, or DHT alone did not exert significant effects on either overall size of BUGs or epithelial growth and ductal branching. All-trans-RA at 10-6 M decreased the [3H]-thymidine labelling index of mesenchyme of BUGs cultured in medium with DHT plus insulin or DHT alone, but did not decrease the [3H]-thymidine labelling index of epithelium. The present results indicate that TGF-beta1 inhibits androgen-induced epithelial and mesenchymal growth as well as epithelial morphogenesis of BUGs from neonatal mice. Such an inhibitory effect of TGF-beta1 is not mimicked by All-trans-RA at physiological concentrations.