We measured plasma concentrations of soluble receptors for IL-2 (sIL-2R) and tumour necrosis factor-alpha (TNF-alpha) in 149 haemophilia patients. Soluble IL-2R levels were elevated in 37% of 62 HIV-seronegative patients (mean 570 +/- 27 U/ml versus 361 +/- 17 U/ml in the control group, P less than 0.0001), in 78% of 68 HIV-seropositive patients (928 +/- 49 U/ml, P less than 0.0001), and in 95% of 19 AIDS/ARC patients (1578 +/- 199 U/ml, P less than 0.0001 compared with controls and with HIV-seronegative patients; P less than 0.005 compared with HIV-seropositive asymptomatic patients). A negative correlation was observed between sIL-2R, relative and absolute numbers of CD4+ cells (P less than 0.0001), and CD4/CD8 ratios (P less than 0.0001). There was also a negative correlation between sIL-2R in plasma and the cellular expression of IL-2R (P less than 0.001). We found a significant association of sIL-2R and plasma neopterin (P less than 0.0001). With progression of the disease from HIV-seronegative to seropositive without symptoms and to full manifestation of AIDS/ARC, sIL-2R plasma levels increased. The highest levels were found at the time of diagnosis of AIDS/ARC, but the levels decreased again during the following 18 months. Eight per cent of HIV-seronegative patients, 32% of HIV-seropositive patients, and 24% of patients with AIDS/ARC had increased plasma TNF-alpha. We conclude that sIL-2R and TNF-alpha plasma levels are elevated in HIV-infected haemophilia patients and that sIL-2R is a marker for disease progression from asymptomatic HIV-seropositive to AIDS/ARC.