OBJECTIVES: To examine the impact of high-dose multiple micronutrient supplementation on survival and disease progression among HIV-infected individuals in Thailand. DESIGN: Randomized placebo-controlled trial. METHODS: Four-hundred and eighty-one HIV-infected men and women living in and around Bangkok with CD4 cell counts in the range 50 x 10(6)- 550 x 10(6)/l were randomized to receive micronutrients or placebo for a period of 48 weeks. Trial participants were examined clinically 12-weekly and tested for CD4 cell count 24-weekly. A subset were tested for HIV plasma viral load at 48 weeks. RESULTS: Seventy-nine (16%) trial participants were lost to follow-up and 23 (5%) died. The death rate was lower in the micronutrients arm with the mortality hazard ratios [95% confidence interval (CI)] of 0.53 (0.22-1.25; P = 0.1) overall and 0.37 (0.13-1.06; P = 0.052) and 0.26 (0.07-0.97; P = 0.03) among those with CD4 cell counts < 200 x 10(6)/l and < 100 x 10(6)/l respectively. There was no impact on CD4 cell count or plasma viral load. CONCLUSIONS: Multiple micronutrient supplementation may enhance the survival of HIV-infected individuals with CD4 cell counts < 200 x 10(6)/l. This could have important public health implications in the developing world where access to antiretrovirals remains poor. The clinical findings need to be reproduced in other settings and the mechanism, which appears to be independent of change in CD4 cell count, merits further investigation.