Recently, homocysteine levels have been reported to be elevated in young male schizophrenic patients. Since smoking, obesity, low folate or low vitamin B12 and various medications can increase homocysteine levels, we studied these variables and other clinical variables in 258 schizophrenic patients. A multiple linear regression for plasma homocysteine was performed on variables that were significantly related to plasma homocysteine. Variables predicting homocysteine levels in schizophrenic patients include gender, plasma folate levels, plasma vitamin B12 levels, mean red blood cell corpuscular volume and diastolic blood pressure. Only 24% of the variance in male patients was explained by the model. The reason for elevated plasma homocysteine in some schizophrenic populations remains unclear.