Cocaethylene (EC), cocaine (COC), and ethanol (ETOH) concentrations were measured in 46 serial plasma samples from 15 male trauma victims. In all but two patients EC was detected on admission to the hospital. In the remaining two, EC was not detected throughout hospitalization. However, these two patients had the lowest ETOH concentrations in the series (200 and 300 mg/L). Plasma concentrations ranged up to 128 micrograms/L for EC, up to 421 micrograms/L for COC, and up to 5,100 mg/L for ETOH. Ratios of EC to COC concentration (EC/COC) were as high as 4.1. Concentrations of EC showed statistically significant correlation with those of COC (p < 0.01). The plasma half-life (T1/2) of EC was found to be longer than that reported for COC (1 h) and was estimated to be 3.5, 4.5, and 5.5 h in three patients.