Viral hepatitis, proven by biopsy in 44 patients known to be drug addicts or confirmed drug takers had serial clinical, biochemical and (half of them) biopsy studies between 1971 and 1974. At the time of the first biopsy the period of addicition averaged 28.8 months. 30 of the 44 patients had had jaundice. At the time of the last biopsy, 20 of the 44 had chronic persisting and three had chronic active hepatitis, i.e. more than half had a chronic form. A further 12 patients had "hippie" hepatitis, a special form of acute viral hepatitis with piecemeal necrosis, histological evidence of possible change to a chronic state. There was no case of complete healing during the period of observation. The high rate of chronic hepatitis is thought to be due to partially insufficient immune response. The clinical and even biochemical course in most of the patients was remarkably mild. Severe clinical forms are rare and were not observed at all in the described group. It would therefore, seem that the prognosis is generally good, in contrast to chronic hepatitis in non-addicts.