Psychiatric symptoms and cognition were assessed in 13 patients with schizophrenia, one patient with schizoaffective disorder, and one patient with psychosis not otherwise specified while they received a conventional neuroleptic and again after an average of 15 months on clozapine. Despite improvements in psychiatric symptoms, attention, memory, and higher-level problem-solving were essentially unchanged. This suggests that certain cognitive deficits are relatively independent of psychotic symptoms in schizophrenia, and are probably central and enduring features of the disorder. Cognitive disability appeared to have been rate-limiting in the sample's rehabilitation, as patients' social and vocational adjustment remained marginal during the study. We also observed that treatment with clozapine was associated with a decline in some memory functions; the potent anticholinergic properties of the drug may have been responsible for this.