Fentanyl concentrations were measured in postmortem specimens collected in 20 medical examiner cases from femoral blood (FB), heart blood (HB), heart tissue, liver tissue, and skeletal muscle. Unique was a subset of 7 cases in which FB was obtained at 2 postmortem intervals, shortly after death (FB1) and at autopsy (FB2). The mean collection times of FB1 and FB2 after death were 4.0 and 21.6 hours, respectively. Fentanyl concentrations for FB1 and FB2 ranged from undetectable to 14.6 microg/L (mean, 4.6 microg/L) and 2.0 to 52.5 microg/L (mean, 17.3 microg/L), respectively. Corresponding mean HB, liver tissue, and heart tissue fentanyl concentrations were 29.8 microg/L, 109.7 mg/kg, and 103.4 mg/kg, respectively. The fentanyl HB/FB1 ratio (mean, 8.39) was higher compared with the corresponding HB/FB2 ratio (mean, 3.48). These results suggest that postmortem redistribution of fentanyl can occur in FB.