Abstract Background Postmortem redistribution (PMR) refers to the changes that may occur in drug concentrations after death. Consequently, postmortem concentrations in blood may not always replicate the antemortem drug levels. Literature supports the model describing drugs with a liver (L) concentration to peripheral blood (P) concentration ratio less than 5 (L/kg) being prone to little or no PMR. Conversely, drugs with a L/P ratio greater than 20 to 30 (L/kg) have propensity for substantial PMR. Findings Expanding upon this prior work, the current paper presents the concept of a postmortem redistribution factor ( F ) for a drug, which characterizes the direct relationship between postmortem peripheral blood and the corresponding antemortem whole blood concentration. Conclusions Development of the concept of a " postmortem redistribution factor" will provide a more definitive and authoritative drug ranking, and possibly, numerical interpretation of PMR for forensic toxicologists.