The treatment of patients with schizophrenia who fail to respond to antipsychotic medications remains a challenge. Despite numerous attempts to establish effective somatic treatment approaches for this population, clozapine appears to be the only well established alternative. Depending upon trial duration and response criteria, between 30% and 60% of previously unresponsive patients appear to derive clinically significant benefit from clozapine. Clozapine also has important advantages in terms of its reduced propensity to produce extrapyramidal side-effects. Agranulocytosis remains an important risk, so strategies to improve the benefit-to-risk ratio should be explored. Issues such as trial duration, dosage, blood levels and predictors of response require additional study.