BACKGROUND In our experience, many of our schizophrenic patients treated with clozapine request the newer atypical antipsychotic agents in order to eliminate the weekly blood monitoring. However, there are few guidelines available to clinicians interested in switching patients successfully treated with clozapine to olanzapine. METHODS The goal of this study was to collect preliminary data on the safety, clinical effectiveness, and predictors of response of switching clozapine patients to olanzapine. In an open trial, 19 patients receiving clozapine were switched to olanzapine. RESULTS Eight (42%) of 19 patients were considered responders. Seven patients decompensated seriously enough to require hospitalization. All 7 of these patients were restabilized on clozapine treatment in the hospital, and olanzapine was discontinued. In an additional 4 patients, clinical status worsened, and clozapine doses were titrated upwards and olanzapine was slowly discontinued. Overall, mean total Brief Psychiatric Rating Scale (BPRS) scores increased significantly from baseline to final assessment (p = .02). Responders had been treated for a significantly shorter period of time with clozapine prior to the switch compared to nonresponders (p = .04) and were receiving a lower dose of clozapine (p = .05). The final olanzapine dose did not differ between responders and nonresponders. All responders have remained on olanzapine treatment and are stable. CONCLUSIONS In this open trial, the crossover from clozapine to olanzapine was generally well tolerated and resulted in a successful transition for 8 of the 19 patients. However, mean scores on the total BPRS and negative symptom and depressive symptom subscales significantly increased. Caution must be taken in determining which patients may benefit from the switch to olanzapine because of the risk of decompensation and hospitalization. Because this was an open trial, these findings require replication in a controlled trial.