Cannabinol and 11-OH-delta9-THC have been detected in the individual urines of five professed marihuana or hashish smokers. Both compounds exist primarily as urinary conjugates with the concentration of cannabinol being substantially greater than 11-OH-delta9-THC in all urines. These findings are discussed in light of present knowledge of delta9-THC metabolism and in view of current analytical procedures for the determination of delta9-THC and its metabolites in physiological fluids.