On the hypothesis that drug addiction may be due to "masked depression", lithium was administered to 20 opiate addicts. Only nine patients took the lithium carbonate tablets for more than a few weeks; during this period they seemed to abstain from taking opiates. After 1 year, all the patients were off lithium and most of them again took opiates. Due to lack of cooperation on the part of the patients, the observations can neither confirm nor refute our hypothesis. The study shows that psychological and socio-environmental factors make trials on drug treatment of opiate addicts almost impossible to carry out.