From January 1980 to December 1983, 989,907 blood donations were screened for HBsAg. A total of 1,345 was found HBsAg positive; 33 of whom were negative for anti-HBc (2.45%); in 10 cases HBeAg was present at a low level along with HBsAg. 2 of the 33 subjects were lost to follow-up. Late serum samples were available for 28 blood donors, and clinical and biological data only were known for the 3 others. An evolution of HBV markers was observed in each case; anti-HBc antibody became positive in 24 subjects (the 4 remaining subjects had a very short follow-up); HBeAg was positive at a high titer in 18 subjects and seroconversion to anti-HBe was observed in 7 individuals; HBsAg concentration increased in 21 subjects from 2 to 4,000 times and decreased in the 7 others. Seroconversion to anti-HBs was observed in 8 individuals. According to these serological, biological and clinical findings, different outcomes were observed: in 6 subjects too short a follow-up was available to allow appropriate classification, but there was evidence to suggest all probably developed clinical hepatitis; in 6 subjects asymptomatic hepatitis with rapid loss of HBsAg occurred; in 2 subjects asymptomatic hepatitis with the persistence of HBsAg at a low level and seroconversion to anti-HBe occurred; and in 17 subjects clinical hepatitis developed. These observations establish that most of the 33 blood donors were infectious at the time of their blood donation, and that anti-HBc antibody screening must not replace HBsAg screening for blood donations.