Mefloquine is currently the drug-of-choice for malaria prophylaxis among military personnel. Four active duty military personnel receiving 250 mg mefloquine per week were killed in the line of duty under combat conditions. Samples of blood, bile, liver, kidney, muscle, brain, spleen and lung were submitted to the Division of Forensic Toxicology, Office of the Armed Forces Medical Examiner, for routine toxicologic analysis. Qualitative screening revealed only the presence of ethanol (< 25 mg/dl, probably attributable to postmortem formation) and mefloquine. Quantitation of mefloquine was performed using an HP 5880 gas chromatograph equipped with a nitrogen/phosphorus detector. The column was an HP-5 cross-linked 5% phenyl methyl silicone fused silica capillary column (15 m x 0.25 mm i.d. x 0.25 microns film thickness). The temperature program began at 110 degrees C, was held for 1 min and ramped at 20 degrees C/min to 200 degrees C, held for 1 min and then ramped at 10 degrees C/min to 280 degrees C and held for 10 min. Mefloquine elutes with a relative retention time similar to that of the tricyclic antidepressants. No postmortem data concerning mefloquine concentrations or tissue distribution was available. Quantitated blood concentrations in the presented cases were greater than the expected therapeutic values indicating the possibility of postmortem redistribution of this drug. No mefloquine overdoses were identified in the literature making comparison to the postmortem therapeutic concentrations impossible at this time.