Ethanol was determined by headspace gas chromatography (GC). For cannabis, the methods employed were radioimmunoassays (RIAs) for screening and gas chromatography/mass spectrometry (GC/MS) for the determination of delta-9-tetrahydrocannabinol (THC) in blood. The study sample consisted of 1,169 drivers and 225 pedestrians. THC was detected in the blood of 127 driver victims (10.9 percent) in concentrations ranging from 0.2 to 37 nanogram/milliliter (ng/ml), with a mean of 3.1 +/- 5.0 ng/ml. Ethanol was found in 667 driver victims (57.1 percent), in concentrations ranging from 9 to 441 milligram (mg)/100 ml, with a mean of 165.8 +/- 79.5 mg/100 ml. For pedestrians, the incidence of THC and ethanol in the blood was 7.6 and 53.3 percent, respectively. The incidence of THC in the driver victims in this study constitutes an approximately 3-fold increase over the results of an Ontario study completed in 1979. At least a part of the increase may be attributed to interstudy differences in analytical methodology for cannabinoids. 6 tables and 12 references. (Author abstract)