Activation of the inflammatory response system has been reported in schizophrenia. Levels of serum IL-1 receptor antagonist (IL-1ra) and soluble IL-2 receptor (sIL-2R(alpha)) were studied in 32 schizophrenic and 22 age- and sex-matched healthy subjects before and after an 8-week treatment protocol. Psychopathology was assessed with the Positive and Negative Syndrome Scale (PANSS). At weeks 0 and 8, sIL-2R(alpha) levels were significantly higher than in the schizophrenic patients, as well as in a neuroleptic-naive subgroup, than in controls. Patients' sIL-2R(alpha) levels did not vary significantly between weeks 0 and 8. IL-1ra levels in controls did not differ significantly from those in patients at week 0 but were significantly lower at week 8. The patients' serum IL-1ra levels varied significantly between weeks 0 and 8. IL-1ra levels were significantly higher in the subgroup of neuroleptic-naive patients at week 0 than in controls. Levels of sIL-2R(alpha) at week 0 were positively correlated with PANSS positive and negative symptom scores at week 8, and levels at week 8 were positively correlated with PANSS total, positive symptom, and negative symptom scores at week 8. IL-1ra levels at week 0 were positively correlated with PANSS scores at week 8. There were positive correlations between both delta (baseline values minus endline values) IL-1ra and delta sIL-2R(alpha) levels and delta PANSS negative symptoms. The results provide evidence for immune activation in some schizophrenic patients and suggest that medication differentially affects the production of sIL-2R(alpha) and IL-1ra.