Sera of 17 HBeAg positive and 104 anti-HBe positive asymptomatic HBsAg carriers from two cohorts were tested for HBV DNA. HBV DNA was found in 13 of 17 HBeAg positive carriers (76.5%) and in only 7 of 104 of anti-HBe positive carriers (6.7%). Eleven of the 17 HBeAg positive carriers were retested for HBV DNA over a period of 7 to 36 months after the initial test. HBV DNA disappeared from the serum in 2 patients in spite of persistence of the HBe antigen. Of the 104 anti-HBe carriers, 89 were retested for HBV DNA over a period of 6 to 52 months after the initial test. HBV DNA disappeared from the serum in 5 of the 7 who were previously positive for HBV DNA, and persisted in 2. These findings indicate that there is an inconstant relationship between the time of seroconversion of HBeAg to anti-HBe and the disappearance of HBV DNA. In one HBeAg positive patient, HBV DNA, which was absent in the serum on first testing, was present on retesting. This suggests that the presence of HBV DNA in the serum of some patients may be intermittent. The presence of HBV DNA in the serum of some anti-HBe positive carriers accounts for the finding that they may be infective. All but one of the HBV DNA positive anti-HBe carriers were born outside North America, most in Asia. HBV DNA were found more frequently in the serum of anti-HBe positive carriers who had biochemical and histological evidence of liver disease than in carriers without such evidence.