- Homocysteine is a neurotoxic amino acid originally found to be an independent risk factor for cardiovascular and cerebral vascular disease and more recently suggested to be a risk factor for Alzheimer's disease. Several authors have observed high plasma homocysteine levels among schizophrenia patients. We reported that such high levels characterize young male schizophrenia patients. We now studied two groups of schizophrenia patients (N= 41) and controls (N= 29) for CSF homocysteine levels. No difference was found for CSF homocysteine levels between schizophrenia patients and controls (p=. 041 for Study A and p=. 52 for Study B).