The diabetes mellitus and arterial hypertension are among the most significant pathologies conditioning disorder of excretion of protein with urine. These very diseases are mostly dangerous for kidneys. Therefore, important significance has the search of early manifestations of damage of kidneys in patients with these diseases. The microalbuminuria is one of early manifestations of affection of kidneys in patients with diabetes mellitus and arterial hypertension. Only this early (pre-clinical) stage of affection of kidneys is the only reversible one in case of prescription of medicinal therapy. Nowadays, factually all applied diagnostic test-systems for detection ofmicroalbuminuria are based on immunological half-quantitative and quantitative detection of concentration of human serum albumin in urine. In this study was applied new recombinant human serum poly-peptide A3 from strain of streptococcus group G isolated from cow milk. The human serum albumin-binding capacity of poly-peptide A3 was analyzed in comparison with poly-peptide A2. Previously, recombinant human serum albumin-binding poly-peptide A2 was primarily applied in test-system for detection of microalbuminuria instead of commonly used antibodies. The analysis of 'human serum albumin-binding capacity of recombinant human serum poly-peptide A3 and A2 demonstrated that both of them can interact with human serum albumin in solution and adsorbed condition. This characteristic permitted applying poly-peptide A3 in immobilized form in qualitative test-system for detecting microalbuminuria. The actual study also propose specific and sensitive technique of screening and monitoring of patients with diabetes mellitus and arterial hypertension. The mentioned technique used tagged human serum albumin-binding polypeptide A3 combined with microchip technology. The comparison of test-systems using recombinant poly-peptides A3 and A2 established that application of poly-peptide A3 in test-system permits to detect more precisely concentration of human serum albumin in urine samples. The test-system of this kind was successfully implemented for both detection and qualitative identification of microalbuminuria in patients with diabetes mellitus and arterial hypertension.