Six overlapping genomic regions of capsid proteins VP1 and VP3 of hepatitis A virus (HAV) inserted into the expression vectors pBD or pUR respectively expressed beta-galactosidase-HAV fusion proteins. The recombinant proteins were poorly soluble so they were difficult to detect by human anti-HAV sera in radioimmunoassay, but the fusion proteins dissolved in sodium dodecyl sulfate reacted with human and rabbit anti-HAV-positive sera in immunoblots. Antisera against VP1 and VP3 recombinant proteins reacted with the respective structural proteins of HAV in immunoblots. Two recombinant proteins, one including the first 120 amino acids of the N-terminus of VP1 and the other containing all of VP1 except for the first 60 N-terminal amino acids, induced a transient neutralizing antibody response in rabbits. Antisera directed against other regions of VP1 and VP3 neither neutralized viral infectivity nor recognized native virus in a competitive radioimmunoassay. However, when immunized animals were challenged with a sub-immunogenic dose of HAV, all animals responded with stable virus-neutralizing antibodies.