Quetiapine (Seroquel) is an atypical antipsychotic drug belonging to a new chemical class, the benzothiazepine derivatives. We present three cases from the Provincial Toxicology Center of British Columbia, Canada in which suicidal overdose deaths were associated with quetiapine. The blood specimens were initially subjected to a thorough qualitative analysis. Basic drugs were screened for by liquid-liquid extraction followed by gas chromatography-nitrogen-phosphorus (GC-NPD) and gas chromatography-mass spectrometry-electron impact detection utilizing both in-house and commercial search libraries. Acidic and neutral drugs were screened for by liquid-liquid extraction followed by high-performance liquid chromatography-diode-array detection. Volatiles were assayed by gas chromatography-flame-ionization detection. Quetiapine was assayed in biological specimens by basic extraction with n-butyl chloride and derivatized with 50 microL of MTBSTFA and separation by GC-NPD. Linearity was observed up to 2.0 mg/L. Samples with concentrations exceeding the linearity were diluted. These cases were chosen for study because they were all deaths as a result of suicidal ingestion of drugs in which quetiapine was considered a significant factor. The concentrations of quetiapine in these cases are 6-16 times greater than the upper reported therapeutic range (0.1-1.0 mg/L). In case #1, the concentrations of quetiapine found were 7.20 mg/L (19 micromol/L) in blood and 0.93 mg/L (2.4 micromol/L) in vitreous fluid. In case #2, the concentrations of quetiapine found were 16 mg/L in blood (42 micromol/L), 120 mg/kg (310 micromol/kg) in liver, and 1.8 mg/L (4.6 micromol/L) in vitreous fluid. In case #3, the concentrations of quetiapine found in femoral blood was 5.90 mg/L (15 micromol/L). In all cases, drugs in addition to quetiapine were detected, but in cases #1 and #2, the cause of death was considered to be a quetiapine overdose and the other drugs were not considered to be contributory. Case #3 was considered a mixed drug overdose.