The objective of this study was to determine whether beta 2-microglobulin, neopterin, nutritional status, clinical status, immunosuppression, and hematologic status are predictors of human immunodeficiency virus (HIV)-related wasting and wasting syndrome. In addition, we aimed to determine which factors are early predictors and which are late predictors of wasting. For this cohort study of HIV-1-seropositive men seen semiannually from 1984 to 1991, a nested case-control design was used to analyze the predictive value of independent variables collected at baseline (first study visit for the seropositive cohort, first seropositive visit for seroconverters), 12 to 18 months prior, 6 to 12 months prior, and less than 6 months prior to the time at which case patients and control subjects were identified. Data on beta 2-microglobulin, neopterin, educational status, and diet were only available at baseline. A total of 41 case patients and 161 control subjects (n = 202) were identified. These were homosexual/bisexual men who were either HIV-seropositive on entering the study (n = 177) or who seroconverted during the study period (n = 25). Case patients were defined as men who had lost more than 10% of their baseline weight or who had a clinical diagnosis of wasting syndrome using the 1987 Centers for Disease Control definition. Control subjects had less than 5% weight loss from baseline or no weight loss at all. Four control subjects were matched to each case patient (where possible) by age and duration of follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)