Follicle-stimulating hormone (FSH) is involved in the regulation and maintenance of gametogenesis. It exists in multiple molecular forms with different oligosaccharide structures which in turn are influenced by the hormonal milieu. Previous studies from our laboratory demonstrated that antiandrogen administration to immature male rats altered the biological activity and the distribution profile of pituitary FSH isoforms. The aim of this study was to examine possible modifications in pituitary FSH polymorphism throughout sexual development (10-, 32- and 75-day-old rats). In addition, the effect of androgen deprivation by castration (32-day-old rats) and its replacement with a nonaromatizable androgen - dihydrotestosterone - on pituitary FSH polymorphism was determined. Concanavalin A affinity chromatography was used to isolate groups of FSH isoforms according to their carbohydrate inner structure. Radioimmunoassay and Sertoli cell bioassay were used to evaluate FSH immuno- and bioactivities. Androgen rise in serum was accompanied by a marked increase in pituitary bio- and immuno-FSH content in 32- and 75-day-old rats. However, FSH pituitary content did not vary despite the significant increment observed in serum FSH levels after castration and decrease to control levels after androgen replacement. The distribution profile of immuno- and bioactive FSH changed throughout sexual maturation. The proportion of pituitary FSH isoforms bearing complex oligosaccharide structures (triantennary, bisecting, complete and truncated biantennary) increased with age, with a concomitant decrease in the proportion of isoforms bearing incomplete carbohydrate chains. The distribution profile observed in castrated 32-day-old rats was similar to that determined in 10-day-old animals. Androgen replacement restored the distribution profile to normal. These results suggest that androgens regulate the incorporation of sugar residues to the carbohydrate chains of pituitary FSH favoring the biosynthesis of complex-type oligosaccharide structures.