Twenty-nine in-patients with acute schizophrenia were examined to assess serum neopterin levels by ELISA at two points of time: during the state of acute symptoms and after clinical recovery at the point of discharge (at an interval of 30.84 +/- 15.22 days). Patients showed significantly higher levels of neopterin than controls. Moreover, the neopterin levels were significantly higher in patients after clinical improvement than in acutely ill patients. Neopterin levels in patients after clinical recovery were negatively correlated to scores of psychopathological symptoms, and positively to neuroleptic medication at the acute stage of the disease. The increase of serum neopterin during treatment of schizophrenia may reflect an up-regulation of dopamine turnover, rather than immunological activity.