The relationship between tumour necrosis factor-alpha (TNF-alpha) and the interleukin-2 (ILL-2) system in HIV-1 infection is important in understanding the dynamics of early immune response before the development of acquired immunodeficiency syndrome. Levels of TNF-alpha, IL-2 and soluble IL-2 receptor (sIL-2R) in serum and cerebrospinal fluid (CSF) samples from 31 asymptomatic HIV-1 seropositive individuals were measured. High levels of TNF-alpha were detected in CSF of 17 (55%) and serum of 22 (71%) subjects, 15 (88%) of whom had elevated CSF IL-2 levels and 16 (94%) had high sIL-2R levels. Moreover, CSF levels of TNF-alpha significantly correlated with CSF levels of IL-2 and sIL-2R. TNF-alpha, IL-2 and sIL-2R seem to be released within the intrathecal compartment early in the course of HIV-1 infection. In view of the known cytotoxic effects of TNF-alpha, an early release may contribute to subsequent development of neurological complications.