The preS1 domain of hepatitis B virus envelope proteins contains a site of attachment to the hepatocyte membrane that has been shown to evoke virus-neutralizing antibodies. Using synthetic peptides, we have examined kinetics and specificity of the anti-body response to preS1 during acute and chronic HBV infection. Antibodies against two continuous B cell epitopes, p (21-32) and p (32-47), which overlap with the virus receptor for hepatocytes, were detected in 17 (28%) and 28 (47%) patients, respectively, of 60 patients who were tested during acute hepatitis B. Serial testing demonstrated these anti-preS1 specificities in more than 50% of patients who became virus free. By contrast, five patients with chronic evolution of hepatitis B and 61 of 66 patients with an established chronic HBV infection were negative, independent of serological profile and liver disease activity. Fifteen (22.7%) patients with chronic hepatitis B were positive for antibody to the C-terminus p (94-117) preS1 sequence that, unlike the acute-phase anti-(21-32) and anti-(32-47) reactivities, did not behave as a virus-precipitating antibody. Acute-phase sera were found to also contain virus-precipitating antibodies directed against conformational preS1 epitopes. These results indicate that the preS1 site, which contains the binding activity for the hepatocyte membrane, elicits an early antibody response during acute hepatitis B. A defect in such antibody repertoire may participate in the chronicity process as a result of continuing reinfection of hepatocytes by circulating virions.