“Nonparenteral” transmission of acute viral hepatitis was implicated in 50.5 per cent of 346 patients included in this study and in 67.5 per cent of 1,235 cases reviewed for the period 1969–1973. Hepatitis B surface antigen (HBSAg) was detected in 48.3 per cent of these patients. Of 476 family contacts of HBSAg carriers 71 per cent had HBSAg or anti-HBS, this being true for 88.8 per cent of siblings and for 67.7 per cent of offspring. Anti-HBSwas detected in 10.4 per cent to 49.3 per cent of the populations tested, its frequency correlating with that of HBSAg and increasing with age. Significant differences in the patterns of exposure to the hepatitis B virus (HBV) were seen between offspring and siblings of HBSAg carriers mainly determined by the observed HBSAg prevalence in relation to their age. It was calculated that as many as 25 per cent of all Greeks may come into familial contact with HBSAg carriers and acquire the infection mainly by nonparenteral mechanisms. It is concluded that in Greece there is already a wide exposure to HBV before adulthood and that this should be borne in mind when considering possible future vaccination programs.