Serum concentrations of androgens, cortisol, androgen binding proteins, pituitary hormones, together with anthropometric variables and sports performance were studied in two different elite male ice hockey teams. One of the teams (DIF, n = 22) participated in a special dietary program including reduction in fat from approximately 40 per cent of total energy intake (E%) to less than 30 E% and an increase in carbohydrate intake from 45 E% to about 55 E%, while the other (SSK, n = 21) served as a control group and had no special dietary program. The study covered a 7-month period. Basal values of serum testosterone, sex hormone binding globulin (SHBG), non-SHBG-bound testosterone (NST), cortisol, dehydroepiandrosterone sulfate (DHAS) and LH did not differ between the two teams. Serum concentrations of testosterone, SHBG, NST and cortisol increased significantly during the study period in the DIF group and were, with the exception of SHBG, significantly higher than in the SSK group at the end of the study (33.0 vs 26.8 nmol/l, p less than 0.05; 22.5 vs 18.3 nmol/l, p less than 0.05; and 548 vs 464 nmol/l, p less than 0.01). The ratio between NST and cortisol which was used as an index of anabolic/catabolic steroid balance did not change in either group during the study. A significant decrease in the serum concentrations of LH during the observation period was found in the SSK group. The endocrine differences between the teams may be explained by a relative negative energy balance in DIF, together with a reduced fat and increased carbohydrate intake.(ABSTRACT TRUNCATED AT 250 WORDS)