The sexual development of normonatriophilic (Normo) and hypernatriophilic (Hyper) male Wistar rats was compared from 30 to 60 days of age (N = 8-10 per group) with emphasis on the onset of puberty. Hyper rats (more than 5 ml of saline a day in a situation of free access to tap water and 1.5% NaCl) had a 20-39% body weight reduction and a 22-29% testicular growth rate decrease compared to Normo rats. Plasma testosterone (ng/ml) of Normo rats increased from 0.29 +/- 0.02 at 30 days to 1.42 +/- 0.18 at 50 days, decreasing to 0.87 +/- 0.15 at 60 days of age, with no significant difference compared to Hyper animals. Plasma concentration (ng/ml) of luteinizing hormone (LH) was significantly lower in Hyper (0.21 +/- 0.03) than in Normo (0.43 +/- 0.06) rats at 40 days. At 30 days, plasma follicle stimulating hormone (FSH) levels (ng/ml) were significantly higher in Hyper (18.9 +/- 1.3) than in Normo (15.6 +/- 0.5) rats. It is possible that increased levels of FSH compensated for a reduced amount of LH, thus allowing similar testosterone production by Hyper and Normo rats. At 30 days, testis maturation was higher in Hyper rats, as indicated by a 22% increase in tubular cross-sections with young spermatids. At 50 days, spermatogenesis progressed to the production of mature spermatids (onset of puberty) and Hyper rats exhibited an 18.7% lower rate of testis maturation. Testis maturation was similar in Hyper and Normo rats at 60 days.