The straight line nucleic acids detection method of viruses and wide spectrum of virus antigens immunodiagnostics in acute hepatitis of unknown etiology patients has allowed verifying the diagnosis at 19% cases (a viral hepatitis A, C or E). Results of research do not allow to consider hepatotropic viruses HGV, TTV, PV B19, EBV, CMV, HHV 1, 2, 6 and 8 type, NV-F as etiological agents at the majority of patients of investigated group, and the data of the anamnesis and a clinical and laboratory picture of a current of disease does not allow to exclude at 29.4% of patients a drug-induced hepatitis. Despite detailed molecular-biological and immunological inspection of patients, at 37.9% of acute hepatitis of unknown etiology patients it was not possible to establish a connection with hepatitis and defined etiological factor (the infectious agent).