Proteolytic activity of Lactobacillus helveticus A75 and effects of caseins hydrolysis by this strain on their immuno-reactivity were studied. Proteases of L. helveticus A75 hydrolyzed both alpha(S1)- and beta-caseins and were inhibited by serine-and metalloproteases inhibitors. Polymerase chain reaction amplification revealed the presence of prtH gene, which was 99% identical to prtH gene of L. helveticus CNRZ 32. Effect of proteolysis of alpha(S1)- and beta-caseins by L. helveticus A75 on their immunoglobulin E (IgE) binding ability was studied by an enzyme-linked immunosorbent assay with the pool of eight sera from cow milk allergy patients. The IgE binding ability of hydrolyzed proteins was lower than that of intact proteins, which indicates that hydrolysis of alpha(S1)- and beta-caseins by proteases of L. helveticus A75 decreases their recognition by specific IgE. Half maximal inhibitory concentration values were 2.01 and 2.28 mu g/mL for alpha(S1)- and beta-casein, respectively, and increased until 9.08 and 13.65 mu g/mL, respectively, after their hydrolysis by L. helveticus A75.