Control tests and subsequent comparative analysis of their results related with the detection of anti-hepatitis C virus (anti-HCV) by different ELISA systems were made at a laboratory of the "Vector-Best" Company, Novosibirsk (A), a clinical diagnostic laboratory of Infection Clinical Hospital No. 1, No. 1 (B), and at a laboratory of chronic viral infections of Andjaparidze Institute of Viral Drugs of the Russian Academy of Medical Sciences (C). Two thousand three hundred and fifty blood sera of donors and 236 blood sera of patients with acute and chronic renal pathology were examined. The comparative research made at the above facilities by different ELISA systems produced diversified results. An analysis of 2350 blood samples from donors made in 3 ELISA systems at laboratory A showed divergence in 19 (0.8%) cases. At laboratories B and C, 5 ELISA systems (a set of 236 samples) denoted differences in 28 (11.9%) cases. Significant variances were registered in confirmation of disputable results of ELISA with immunoblot, which is apparently related with differing criteria applicable to confirming the positive results from using the confirmative tests. A possibility is discussed of using different ELISA systems in screening examination.