['To examine baseline hormonal concentrations and the pharmacokinetic response on day 0 and day 28 of 28 days of androstenedione supplementation.', 'Eight men (mean (SD) age 44.1 (3.0) years (range 40-48), weight 76.3 (9.4) kg, and percentage body fat 20.6 (6.7)) participated in a randomised, double blind, cross over, 2 x 28 day placebo controlled study. Subjects were tested on day 0 and 28 days after receiving 200 mg/day oral androstenedione and a placebo treatment with a 28 day washout period between treatments. Serum hormone concentrations were examined at baseline (time 0) and then at 30 minute intervals for 180 minutes to measure day 0 and day 28 pharmacokinetic responses. Analytes included androstenedione, total testosterone, dehydroepiandrosterone sulfate (DHEAS), oestradiol, and sex hormone binding globulin (SHBG). Lipid concentrations, weight, body composition, resting heart rate, and blood pressure were also measured.', "Analysis of integrated area under the curve (AUC) and time 0 hormonal concentrations by repeated measures multivariate analysis of variance (p<0.05) and Fisher's post hoc analysis showed a significant increase in AUC for serum androstenedione at day 0 (108.3 (27.6) nmol/l) in the supplemented condition as compared with day 28 (43.4 (13.1) nmol/l) and placebo (2.1 (0.8) nmol/l) conditions. No other significant AUC changes were noted. After 28 days of supplementation, DHEAS levels were significantly elevated (p = 0.00002) at time 0 (12.9 (1.3) micro mol/l) compared with placebo (7.0 (0.8) micro mol/l) with a trend (p = 0.08) toward elevation of time 0 androstenedione concentrations (16.4 (7.0) nmol/l) compared with placebo (5.6 (0.4) nmol/l). No changes were found for lipids, resting heart rate, or blood pressure, weight, or percentage body fat."] Does four weeks of androstenedione supplementation diminish the treatment response in middle aged men?