Fingernail clippings were obtained from 26 consenting patients of the Glasgow Drug Problem Service (Scotland). At the time of sampling, the participants provided answers to a questionnaire regarding their drug use patterns. Samples were decontaminated by sonication in sodium dodecyl sulfate (SDS), deionized water, and methanol; and the methanolic washes were screened for analyte presence. The washed nail clippings were then hydrolyzed and extracted. Radioimmunoassay (RIA) was used for the screening and high-pressure liquid chromatography (HPLC) for the confirmation of morphine. Positive RIA results were obtained with nail clippings from 25 of the 26 heroin users. The levels ranged from 0.06 to 4.69 ng/mg, with a mean morphine concentration of 1.67 ng/mg. HPLC results were positive for 22 of the 26 nail samples. The mean morphine level by HPLC was 2.11 ng/mg with a range from 0.14 to 6.90 n/mg. Based on these results, the authors suggest that fingernails have the potential of becoming a powerful alternative to hair for the detection of past heroin use in forensic cases. 2 tables, 3 figures, and 16 references