Of samples taken from the left and right ventricles of the heart and the blood vessels in a leg, samples from the left ventricle had the highest concentrations of morphine; and those from the leg blood vessels had the lowest concentration of morphine. The authors conclude that concentration values for morphine, whether measured as free or total morphine, will be higher in samples taken in or near the heart compared with samples taken from peripheral blood vessels. The study involved 76 suspected heroin-related deaths that occurred from September 1, 2002, through April 7, 2003, in New Mexico. Of these 76 cases, 44 (58 percent) tested positive for morphine and morphine metabolites. These cases were the focus of the examination of morphine concentrations in the samples taken at autopsy. Blood samples from all locations on the bodies were processed the same way. The authors advise that factors other than the sampling site can affect concentration measurements, such as a lack of postmortem stability of either the drugs or the specimens, specimen volume, and types of aspiration that draw blood from various parts of the body. Suggestions are offered for future research. 3 tables, 4 figures, and 15 references