-We have examined the effect of a medroxyprogesterone therapy in HIV-infected patients under appropriate nutrition for anabolism. The experiments were performed on 12 men (mean age 40 y), HIV seropositive but free of any clinically active opportunistic infection for at least one month. The patients underwent a 2-week baseline diet period (1.2 g protein·kg -1 body weight (BW)·d ). Indeed HIV-infected patients showed deficiencies in these amino acids. They were randomly divided into groups I and II under double-blinded condition. Group II was given medroxyprogesterone acetate (0.4 g·d -1 ) during the last 3 weeks whereas group I received a placebo. All the patients significantly increased their body weight (P < 0.05) during the experimental periods. Those under medroxyprogesterone tended to show a higher but not significant weight gain (+3.1 ± 1.0 kg in group II and +1.9 ± 0.3 kg in group I). Blood free amino acids were used as rough indicators of amino acid utilization and were analyzed prior and during acute 150 min intravenous infusion of a complete glucose-amino acid mixture. This test was done before and at the end of the experimental periods. Basal essential blood free amino acids were similar in the two groups and did not change during the experimental period. Most essential amino acids increased Reprod. Nutr. Dev. 43 (2003) 203-214 203