The prevalence of HBsAg, anti-HBs, and anti-HBc in the sera of 217 patients with the two polar types of leprosy and 382 hospital controls was studied in order to investigate the degree of exposure of Greek leprosy patients to HBV and the ability of these patients to clear HBV from the blood. Two distinct serological patterns were analyzed: effective exposure, characterized by the presence of one or more of the three serological markers, and active infection, characterized by the presence of HBsAg. From the statistical analysis it was found that TT as well as LL cases had a higher prevalence of effective exposure in comparison to controls (p less than 10(-5) and p less than 10(-6)). No significant difference was found between the two polar leprosy types (p greater than 0.30) or between bacteriologically positive and negative LL cases (p greater than 0.30). As far as the prevalence of active infection is concerned among the effectively exposed subjects of all groups, no significant difference existed between TT cases and controls, LL cases and controls, the two polar leprosy cases combined and controls, the two polar leprosy groups, and LL cases positive and negative for Mycobacterium leprae (p for all comparisons greater than 0.30). It is concluded that leprosy cases are at a high risk of HBV infection, but the prevalence of active infection among those effectively exposed does not differ between leprosy cases and hospital controls.