Abstract By means of radioimmunoassay-technique, hair samples of users, drug related fatalities, carcinoma patients receiving morphine and of experimental guinea pigs receiving codeine were investigated for opiates. The RIA-investigations require a minimum of material; our routine procedures need only 50 mg of hair. No correlation existed between administered doses of opiates and their concentrations in hair of both human and experimental animals. By sectioning the hair, the approximate period of drug use in man could be detected. However, these findings could not be confirmed by the animal experiments. The growth rate of the hair, diffusion and adhesion processes may influence the transport of drugs along the hair. External contaminations and washing procedures were shown to increase or diminish the drug concentration of the samples.