This short-term, single-blind, pilot trial was initiated to investigate the usefulness of quetiapine therapy in the treatment of schizophrenic patients refractory to first-generation antipsychotics. Following a neuroleptic-free period prior to study entry (at least 1 week for oral formulations and 6 weeks for depot formulations), quetiapine was started at 50 mg/day and titrated up to 500 mg/day by Day 6. This 500 mg daily dose was then maintained or increased up to a maximum of 750 mg/day, at the discretion of the treating physician, who was aware of the antipsychotic prescribed. Efficacy measures were represented by changes in total and component PANSS score from baseline to different intervals. Safety and tolerability were evaluated by monitoring the spontaneously referred moderate-to-severe adverse events, changes from baseline in SAS, BARS, and AIMS scores, supplementary use of flurazepam, lorazepam, and benztropine, clinically relevant physical changes, abnormalities in vital signs, blood chemistry, and hematology, and modifications in QTc interval and body weight. Rating scale assessments, categorization of adverse events, determination of physical examination, vital signs, and body weight were performed by a qualified physician blind to the particular antipsychotic under investigation and the aims of the study. All 12 patients completed the 4-week quetiapine treatment course. Mean total PANSS scores were significantly reduced between baseline and study endpoint (p=0.006). Five out of six PANSS subcomponent scores also showed significant decreases (p < 0.05). Six patients showed a reduction of > or = 20% in PANSS total score by the final day of quetiapine treatment, so were classified as responders. There were responders in all schizophrenia diagnostic subgroups (undifferentiated, paranoid, and disorganized). Two patients reported moderate adverse events. One patient received 3 days of benztropine therapy for EPS and five received flurazepam for insomnia. Weight change was minimal and mean SAS, BARS, and AIMS scores all showed nonsignificant decreases between baseline and endpoint. The 50% quetiapine response rate reported here in refractory patients is comparable with those previously reported for other atypical antipsychotics in populations of both refractory and intolerant patients.