Several small short-term intervention studies have suggested that β-carotene supplementation in HIV-infected patients can increase the number of various immune cells including CD4 cells. This prospective double-blinded study was designed to investigate whether β-carotene supplementation would result in this immuno-enhancement in a larger number of patients over a longer time period. HIV-positive patients were randomly assigned to receive either 60 mg β-carotene orally three times daily or a matched placebo. In addition, all patients received a multivitamin supplement. Patients were evaluated at baseline, 1 month, and 3 months for T-cell quantitative subsets, natural killer cells, HIV p24 antigen, β-carotene levels, complete blood counts and chemistry batteries. Body weights and Karnofsky scores were evaluated at each visit. Seventy-two patients signed informed consent forms and entered the study. Except for serum β-carotene concentration, there were no statistically significant differences (P Discussion: Earlier studies suggesting that β-carotene supplementation increased levels of immune cells in HIV-infected patients were not replicated in this study. The addition of a multivitamin supplement to both arms of this study may have masked any difference between the two groups. However, on the basis of the results of this study, we would not recommend supplementation with high doses of β-carotene for HIV-infected patients.