To clarify the relationship between the pre-S antigens and other serological markers of hepatitis B virus (HBV) replication, we followed up 27 patients: 21 presented with symptoms of acute hepatitis (two progressed to chronicity) and six suffered from chronic hepatitis. Pre-S1, pre-S2, HBV DNA, IgM antihepatitis core antigen (HBc), hepatitis B e antigen (HBeAg), and anti-HBe were detected in about 200 sera serially collected at different times for at least 6-12 months from the onset of clinical observation. In the early symptomatic phase of acute hepatitis, the pre-S1 and pre-S2 antigens were present in 95% of the cases and correlated well with high levels of alanine-transferase (ALT) and IgM anti-HBc, while HBV DNA was present in the sera of only six (28.6%) patients (P less than 0.0001). This was the first marker to disappear (1 month after the initial stage). All of the HBV DNA-positive patients were also HBeAg positive, whereas no HBeAg-negative subjects were found with serum HBV DNA. In the six chronic patients, pre-S antigens were always present independently of the HBeAg/anti-HBe status; HBV DNA was detected in three of them, even if transiently, and in two of these it reappeared together with pre-S2 epitope. The follow-up data suggest that, in acute hepatitis, the clearance of pre-S antigens can be considered as a prognostic index of clinical resolution and that, in chronic hepatitis, the persistence of pre-S antigens seems to indicate progression of the disease. In particular, pre-S2, in patients in whom it is intermittent, can be considered as an index of reactivation.