 Schizophrenia and bipolar disorders are major public health problems. The second generation anti-psychotic drugs have efficacy for both positive and negative symptoms and a favorable risk profile as far as movement disorders. However, these drugs are associated with clinically significant weight gain and metabolic effects. The underlying mechanisms of these side effects are unclear, however in our preliminary studies with schizophrenic patients on atypical anti-psychotic drugs, we found that weight gain and vitamin D deficiency was present in about 50 of this population. Given the considerable heterogeneity among the patients on atypical anti-psychotics and potential for weight gain in vitamin D-deficient states, we propose that patients with schizophrenia who gain weight on atypical antipsychotic medications are vitamin D-deficient. This hypothesis will be tested in patients with schizophrenia receiving second-generation anti-psychotic drugs for a minimum duration of 4 months. Specific Aim: We predict that the patients with schizophrenia, who gain weight with antipsychotic treatment, are vitamin D-deficient compared to the patients who do not gain weight. We will examine circulating levels of serum 25OHD, mRNA transcripts and protein expression of vitamin D receptor VDR and the enzymes, CYP24A and CYP27B, in the white blood cells of the subjects and correlate with BMI and the blood levels of leptin and adiponectin. 