Studies were conducted to evaluate the effects of neonatal administration of supraphysiological doses of testosterone on the growth, hormone responsiveness, DNA and protein content, and protein profiles of the epididymis, vas deferens and seminal vesicles in adult mice. Results indicate that in androgenized males, testicular growth (DNA and protein content), circulating and organ androgen levels, and fertility were significantly depressed. The weights of the epididymis, vas deferens, seminal vesicle and kidney, but not that of the spleen, were significantly diminished subsequently to a reduction of protein (all organs) and DNA (epididymis, vas deferens) content. The efficacy of testosterone in promoting accessory sex organs and kidney growth, in adult castrated males, was persistently reduced in neonatally androgenized males. When assessed by DNA content, the response of all organs (except the seminal vesicle) was similar to that of controls, but it was significantly reduced from 16 to 43% when measured in terms of protein content. The protein profiles from seminal vesicles and vas deferens analysed by polyacrylamide gel electrophoresis, showed reproducible persistent alterations which could be reversed by adult androgen therapy.