Neopterin concentrations in body fluids of HIV-1 seropositives provide predictive information. In 1986, we examined serum and urine neopterin concentrations in 29 HIV-1 seropositives. Serum levels of soluble IL-2 receptor (sIL2R), soluble CD8 (sCD8), tumour necrosis factor alpha (TNF-alpha) and circulating immune complexes (CIC) were retrospectively analysed in 1989. All individuals had increased serum and urine neopterin, sIL2R and CIC concentrations, 27/29 had increased sCD8 concentrations, whereas all had normal TNF-alpha levels. During a 3-year follow-up, high urine and serum neopterin concentrations were significantly associated with progression to AIDS and with the occurrence of AIDS-associated death. Both neopterin variables were of similar predictive value (p less than 0.001, generalized Wilcoxon test). sIL2R concentrations were of borderline significance in predicting the onset of AIDS (p = 0.05). All other parameters lacked predictive information in our study. We conclude, that chronic immune activation is detectable in almost all HIV-1 seropositives. Chronic immune activation may be associated with HIV-1 replication and may contribute to the immunopathology of HIV-1 infection.