A method was developed and validated for analyzing 6-monoacetylmorphine, morphine, 6-acetylcodeine, and codeine in routine postmortem liver and kidney specimens using liquid chromatography-tandem mass spectrometry. Samples were prepared with a Stomacher instrument followed by solid-phase extraction. All calibration curves [0.5-1000ng/g] were linear with coefficients of determination greater than 0.99 and limits of quantification of 1.0ng/g. Within-run precision ranged between 2.0% and 8.0%, between-run precision ranged between 1.0% and 9.0%, and accuracy ranged between -5.0% and +3.0%. Matrix effects ranged from -18% to +9%. After matrix effects were excluded, analytical recoveries ranged from 76% to 94%. The distributions of 6-monoacetylmorphine, morphine, 6-acetylcodeine, and codeine were investigated in 31 postmortem cases in which heroin was the primary cause of death. In the current study, the median free morphine ratios were calculated for liver to blood and kidney to blood, which were 2.2 and 4.0, respectively. The current report highlights the importance of testing multiple specimens, including liver and kidney, in heroin-related deaths, especially if no blood samples are available. Furthermore, this work presents new information regarding the distribution of heroin metabolites in liver and kidney.