The Scientific and Practical Center of Dermatovenereology and Cosmetology of the Moscow Department of Healthcare, Moscow, Russian Federation. The investigation of some sera samples for hepatitis B surface antigen (HBsAg) is associated with the problem of results interpretation. The purpose of this study was to describe the problems that arise during the mass screening for HbsAg and to present some ways of their solution in order to prevent false results. Methods. The screening and confirming test systems (TS) for ELISA (including the state modification without the use of a stop reagent) have been applied. The results of screening in ELISA are denoted as the sample positivity coefficient, equal to the ratio of a sample optical density (OD) to the cut-off OD value (S/Co). Results and conclusions. The 545 HBsAg-positive results (1.21 % of screening) have been received by different means of research: 1) after a singular confirming research in 52.29 % of samples; 2) with the OD measurement without a stop reagent in 21.10 % of samples; 3) after diluting 100 and more times in 24.95 % of all HBsAg-positive samples. 17 samples were low-positive in screening (S/Co less than 3); 9 of them were identified as positive, which is 1.7 % of positive samples and 0.02 % of all the samples. Low-positive samples need to be investigated in TS with sensitivity higher than 0.01 ng/ml, because in those with less sensitivity the criteria of positivity aren 't carried out, and the results of blood sera samples research, including those received from pregnant women and newborn children, are interpreted as negative. This is also fair in regards to the research of samples received from the Federal system of research quality assessment.