Immune response of laboratory rodents (guinea-pigs, CBA and Balb/c mice, Wistar and August rats) to inactivated hepatitis A vaccine was quantitatively assessed. Under comparable conditions of experiment, the mice showed the highest antibody titres and were capable of reacting to the lower doses of immunogen; meanwhile their individual variations in immune response were more pronounced; white rats were the least susceptible to the vaccine, demonstrating the minimal antibody formation; guinea-pigs produced antibody at intermediate levels but the antibody titres were the most homogeneous. The enhancing effect of aluminium hydroxide was observed in guinea-pigs examined at the late postimmunization stage. Differences in immunogenicity of three vaccine lots were essentially similar when these lots were tested as undiluted preparations in guinea-pigs and mice for mean antibody titres and in mice for 50% immune response using serial dilutions of vaccine. All three tests could be routinely employed for vaccine immunogenicity control.