In a material of 768 sera obtained from blood donors and patients and 150 sera containing HBs antigen it was investigated whether the available animal sera (horse, swine, goat) with anti-HBs antibodies meet the requirements of diagnostic sera. It was found that none of these anti-HBs animal sera was better than the human serum used as yet. Only the specificity of horse anti-HBs antibodies was equal to the human serum, hence horse serum could be used for diagnostic purposes in routine investigations by the precipitation and complement fixation method. The swine and goat sera did not ensure detection of all HBs antigens which are detected using human or horse serum.