This is a study designed to identify genetic polymorphisms (also called allelic variants or genetic markers) that are associated with response to clozapine. This information will be used to enhance the understanding of clozapine response and side effects. DNA from patients will be examined for significant associations between allelic variants in candidate genes in relation to clozapine effects on positive and negative symptoms, global response, quality of life, relapse rates and side effects.

Patients age 18-65 with a DSM IV diagnosis of schizophrenia who have a history of nonresponse to conventional atypical antipsychotics and who are to be treated with clozapine by their psychiatrist, will be asked to participate at or near the time clozapine therapy is initiated. The Brief Psychiatric Rating Scale (BPRS), Scale for the Assessment of Negative Symptoms (SANS), and the Scale for the Assessment of Positive Symptoms (SAPS) will be performed on all subjects at entry into the study, at 3 weeks, 5 weeks, 8 weeks, and at 4 and 6 months. Adverse effects will be monitored with the Simpson-Angus Scale, Barnes Akathisia scale and the AIMS at each of these time points. The Calgary Depression Scale will also be administered at each visit. A complete neurocognitive assessment battery will be completed at entry and at 6 months for those subjects willing to undergo neurocognitive testing. It is anticipated not all subjects will complete neurocognitive testing. A blood or cheek swab sample will be collected at study entry for DNA analysis. Plasma blood levels will be collected at weeks 3, 5, 8 and study completion for measurement of clozapine plasma concentrations. The subject's weight, BMI, smoking status and concomitant medications will be recorded at each visit.

Inclusion Criteria:

• Diagnosis of schizophrenia
• Beginning clozapine therapy
• age 18-65
• must be willing to participate in interviews and provide a DNA sample

Exclusion Criteria:

• no longer taking clozapine

Psychiatric clinic, Inpatient Psychiatry unit