Heart blood, liver, brain, and femoral muscle taken from rabbits 20 minutes after oral administration of 20 mg/kg cocaine together with 2 g/kg ethanol were kept at 20-25 degrees C for 5 days. Cocaine and cocaethylene concentrations were greatest in the brain, followed by the liver, muscle, and blood; and they showed large intersubject variations at the time of death. Cocaine degraded rapidly in the blood and liver; however, 12.0, plus or minus 8.5 percent, and 26.2, plus or minus 19.4 percent, of the original cocaine was still detectable in the brain and muscle, respectively. Cocaethylene was degraded more slowly than cocaine in all of the specimens. The pH of the blood remained around 7.4 during a 5-day period; all the other specimens showed pH values of 6.2-6.7 on and after the first-day postmortem. When 10,000 ng/g cocaine was incubated with decomposed human blood, liver, brain, and muscle homogenates that contained 0.29-0.60 mg/g endogenous ethanol at 20-25 degrees C and 37 degrees C, no change in cocaine concentration was observed during the study period of 24 hours, and no cocaethylene was detected. The pH values of the homogenates were within the range of 4.2 to 5.2 at the beginning of the experiment. The study found that cocaethylene was more stable in postmortem specimens than cocaine; muscle, as well as brain, was the specimen of choice for detecting cocaine and cocaethylene postmortem; cocaine was resistant to decomposition under acidic conditions; and putrefactive bacteria had no ability to produce cocaethylene even in the presence of cocaine and endogenous ethanol. 2 tables, 3 figures, and 29 references