The transforming growth factor beta s (TGF beta s) affect the metabolic activities of the somatic cells of the testis. Sertoli cells, peritubular/myoid cells, and germ cells contain mRNA for TGF beta 1 and/or TGF beta 2. We have used immunohistochemical techniques to determine, in vivo, when TGF beta 1 and TGF beta 2 are present in the rat testis during development and have identified the precise localization of these growth factors. The most pronounced changes in TGF beta immunoreactivity occurred during spermatogenesis. TGF beta 1 predominated in spermatocytes and early round spermatids, but as the spermatids elongated around stages VIII-IX of the cycle, the TGF beta 1 levels declined. TGF beta 2 was undetectable in spermatocytes and early round spermatids, but as spermiogenesis progressed, around stages V-VI, the spermatids rapidly acquired TGF beta 2. The intense staining for TGF beta 2 was maintained as the spermatids elongated. TGF beta 1 immunoreactivity was detected in Sertoli cells throughout testicular development. TGF beta 2 was found in fetal Sertoli cells, but became undetectable rapidly after birth. In fetal animals the Leydig cells contained TGF beta 1 and TGF beta 2; after birth TGF beta 1 persisted whereas TGF beta 2 became undetectable in the Leydig cells. Prior to puberty, TGF beta 1 and TGF beta 2 were absent in a portion of the Leydig cells; when the adult stage was reached, TGF beta 1 was no longer detectable and TGF beta 2 staining was faint to absent. In conclusion, our novel findings show that TGF beta 1 and TGF beta 2 are present in vivo in testicular cells at clearly defined stages of their differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)