OBJECTIVES: The purpose of this study was to examine the effects of a structured, 8-week, Mindfulness-Based Stress Reduction (MBSR) program on perceived stress, mood, endocrine function, immunity, and functional health outcomes in individuals infected with the human immunodeficiency virus (HIV).DESIGN: This study used a quasiexperimental, nonrandomized design. METHODS: Subjects were specifically recruited (nonrandom) for intervention (MBSR) or comparison group. Data were collected at pretest and post-test in the MBSR group and at matched times in the comparison group. t Tests where performed to determine within-group changes and between-group differences. RESULTS: Natural killer cell activity and number increased significantly in the MBSR group compared to the comparison group. No significant changes or differences were found for psychological, endocrine, or functional health variables. CONCLUSIONS: These results provide tentative evidence that MBSR may assist in improving immunity in individuals infected with HIV.