Clozapine is an antipsychotic without the extrapyramidal adverse effects associated with currently marketed antipsychotics. In animals, this drug has not been shown to induce catalepsy and only weakly antagonizes the stereotypic movements induced by apomorphine and the amphetamines. Clozapine is rapidly absorbed after both single and repeated oral doses, with steady-state concentrations attained within eight to ten days after beginning therapy. It is metabolized to N-oxideclozapine and N-desmethylclozapine, which have less pharmacological activity than the parent compound and are excreted in the urine and, to a lesser extent, in the feces. Clozapine has overall therapeutic efficacy and/or superiority to currently marketed antipsychotics in the treatment of refractory schizophrenia. Usual doses (25–900 mg/d) of clozapine cause fewer extrapyramidal adverse reactions than available antipsychotics. Hypotension, dizziness, salivation, and sedation are the most frequently reported adverse effects and tend to subside over time. Agranulocytosis is the most serious adverse reaction, and those receiving clozapine should undergo weekly white blood cell count determinations. Clozapine is useful for those treatment-resistant patients who have not responded to adequate trials of other antipsychotics.