The possibility was verified of utilizing the determination of specific IgM class antibodies to hepatitis A virus using the method of radiosaturation analysis, for early ethiological diagnosis of hepatitis A. The determination was made using the HAVAB-M kit by Abbott. A high and verifiable presence was found of these antibodies in the first to third weeks of the duration of the disease, positivity was observed up to day 125 from the onset of the diseases. Reliability of the determination of specific IgM antibodies to hepatitis A virus is high. Specific IgM antibodies to hepatitis A, determined using the radiosaturation analysis are a sensitive and specific indicator of the disease. The determination will mainly be used to advantage for identifying patients suffering from the anicteric form of the disease without any clinical manifestations, will substantially improve the ethiological diagnosis of acute hepatitis.