Schizophrenia is a serious neuropsychiatric disease of uncertain etiology. We investigated the seropositivity rate for anti-Toxoplasma IgG and IgM antibodies by enzyme-linked immunosorbent assay (ELISA) in patients with schizophrenia to ascertain a possible relationship between Toxoplasma gondii and schizophrenia. We selected 100 patients with schizophrenia, 50 with depressive disorder, and 50 healthy volunteers to investigate the seropositivity rate of anti-Toxoplasma antibodies by ELISA. The seropositivity rate for anti-Toxoplasma IgG antibodies among schizophrenia patients (66%) was significantly higher than among patients with depressive disorder or healthy volunteers (P < .01). Thus, there might be a causal relationship between toxoplasmosis and the etiology of schizophrenia.