Urinary selenium (Se) concentrations (micrograms Se/l and microgram Se/g creatinine) have been determined in heroin abusers and in healthy controls. Heroin abusers showed significantly (P < 0.050) lower urinary Se concentrations (microgram Se/l and microgram Se/g creatinine) than healthy controls. The decrease of the urinary Se concentration (microgram Se/g creatinine) observed with the increase in age of heroin abusers may be due to the higher exposure to heroin with increased age. No significant differences (P > 0.100) of urinary Se concentrations (both as microgram Se/l and microgram Se/g creatinine) are observed between heroin abusers during methadone treatment and heroin abusers who have stopped taking the drug, with respect to healthy controls.