To evaluate the effects of nutritional supplements on nitrogen and energy balances, body composition and immune parameters, HIV-infected malnourished adult outpatients were prospectively studied. Forty-six patients (4 females and 42 males; 37 +/- 12 y) were supplemented with a polymeric diet (PD) or regular foods (RF) on two consecutive 45-day periods on a crossover design. Weight, skinfold thicknesses, plasma albumin (PA), CD4 and CD8 lymphocyte counts (LC), resting energy expenditure (REE) and urinary nitrogen excretion were measured at baseline, 45 and 90-day. Food intake was weekly recorded by food surveys. Thirty-five patients completed the protocol (18 in Group 1:PD-->RF; 17 in Group 2:RF-->PD). In both groups, weight, fat free mass (FFM), energy balance (EB) and nitrogen balance (NB) increased significantly after PD, whereas LC and PA remained unchanged in both groups. The best results in terms of weight gain were obtained in the PD group and PD plus zidovudine subgroup (n = 8) during the first 45 days (weight gain/FFM gain: 4.8/2.6 kg and 6.8/3.1 kg, respectively). Nutritional supplement with PD, according to the EB and NB goals, was well tolerated and permitted to achieve a significant weight and FFM gain over a 90-day follow-up.