Purified, formaldehyde-inactivated and alum-adjuvanted hepatitis A virus (HAV) vaccines have recently become available for clinical trials. The vaccine is administered intramuscularly in a schedule of 0, 1, and 6 months. The aim of the study was to evaluate the reactogenicity and immunogenicity of an inactivated hepatitis A (HA) vaccine. Three groups of volunteers comprised the study population: 28 volunteers without antibody to HAV were given HA vaccine and, for comparison, 43 subjects received hepatitis B vaccine for possible adverse reactions to the HA vaccine; 12 other subjects received immunoglobulin alone. Each 1 ml dose of HA vaccine contained 720 enzyme units or about 100 ng of antigen. Anti-HAV was determined by means of a commercial assay (Abbott Laboratories: HAV-EIA), and by a more sensitive ELISA. No significant adverse reactions were reported. In the group that received HA vaccine, 4 weeks following the first dose all had detectable antibodies (> or = 20 mIU/ml) by the sensitive ELISA. By commercial HAV-EIA, at 20 weeks following the second dose 75.0% had detectable antibodies, and after the third vaccine all had detectable antibodies. This new inactivated HA vaccine is highly immunogenic and had no significant side effects.