Prevalence of antibodies against hepatitis A (anti-HAV) among young Norwegian drug addicts in 1983 and the relative incidence of specific IgM against hepatitis A (anti-HAV IgM) during the years 1973-1983 have been studied. The survey is based on 1,689 serum samples from 561 persons submitted to hepatitis B screening or clinical hepatitis testing. The prevalence of anti-HAV in such groups was 43% in 1983 versus about 5% in corresponding age groups in the general population and 1% in the Norwegian U.N. soldiers in Lebanon. Presence of anti-HAV clearly correlated with presence of hepatitis B markers. Considerable fluctuations in the incidence of hepatitis A seemed to occur among drug addicts, with pronounced epidemic peaks in 1975 and 1979, coinciding with epidemics in Malm?, Sweden. Though the incidence varied, hepatitis A may have persisted among addicts for some years after 1979 in a semi-endemic manner. Although relatively young, most of them seem to have been in the milieu for some time before catching the infection. Drug addicts seem to be a target group for future hepatitis A vaccination programs.