Persistence of IGM anti-HAV antibody in sera of patients with acute HAV-infection can be followed up to 55 weeks. Available literature does not provide significant information on persistence of IgM anti-HAV antibody in prolonged form of disease. In multi-centric prospective study of the HAV infection prolonged form we have examined persistence of IgM anti-HAV in 30 patients with acute form of disease and 60 patients with prolonged form of disease. The aim of work was to examine length of IgM anti-HAV persistence in sera of patients with prolonged form of disease in relation to sex, length of persistence of sera aminotranspherasis activities and circulating immune complexes and length of secretion of Ag-HAV in stool.IgM anti-HAV, IgG anti-HAV, HBV and HCV markers were determined with ELISA method. Circulating immune complexes were determined with fotometer in the sediment of poliethilenglicol on 480 nm wavelength. Antigen-HAV in stool was prescribe through a method of reversed immunoelectroosmophoresis. Results of examination have shown that the persistence of IgM anti-HAV in sera of patients suffering from acute and prolonged form of disease was first of all continued and than discontinued. In male patients the IgM anti-HAV persistence significantly longer (p < 0.05) in prolonged phase, while in female patients the same goes for acute phase of disease. In prolonged HAV-infection persistence of IgM anti-HAV antibody is three times longer that in acute infection. IgM anti-HAV maintained in sera of patients three times longer than the persistence of sera aminotranspherasis activities and secretion of Ag-HAV in stool, which is proportional to the persistence of circulating immune complexes in sera of patients with acute and prolonged HAV-infection.