Background:Schizophrenia and bipolar disordersare serious neuropsychiatric diseases ofunknown etiology. Recent studies indicated that infectious agents such as Toxoplasmagondii may contribute to some cases of schizophreniaandother mental disorders. In thisstudy we determinedthe prevalence ofT. gondiiinfection and IgGtitersagainstToxoplasmain schizophrenia and bipolar disorder patients andcontrol subjects which comprise firstdegree relatives of the patients and some individuals from neighborhoods.Methods: 214 cases of schizophrenia, 171 patients of bipolar disorders and 363 controlsrecruited fromMeskan and Mareko (Butajira)district forgenetic study in 2001and theirstored sera were analyzed for IgG antibody against T. gondii by using enzyme-linkedimmunoassay (ELISA)for a period of March to May 2009..Results:Overall prevalence of IgG antibodies in all study subjects was 95.2%. Theprevalence of the antibodies increased with age in cases and control subjects. Theseroprevalence ofT. gondii infectionwas 97.7% in patients with schizophrenia,95.3% inbipolar disorder cases and93.7% in control subjects.There was significantly increase inseroprevalence of IgG antibodies toT. gondii in schizophrenia cases comparedwithcontrolgroups (p=0.031) but, the difference in seroprevalence of IgG antibodies was not statisticallysignificant between bipolar disorder cases andcontrols group(p=0.427). In addition, therewas nosignificantdifferenceinIgGtiters betweenthe casesandtheir close relativecontrolsand/or non-relatives controls recruited from neighborhoods.Conclusions and recommendations:patients with schizophrenia had a significantly higherprevalence ofT. gondii infection than the control group. Thus, this study gives additionalinformation to the hypothesis that exposure to Toxoplasma may be risk factor forschizophrenia.Further studies mayberequiredto determine anti-Toxoplasmaantibodylevelin first episode psychosis and in the same individuals in chronic course by follow up tospeculatedecrease in antibodies level caused by antipsychotic or mood stabilizer drugs,whichmight improve the clinical course in the patients.