By using the method of phagocytosis of erythrocytes treated with formaldehyde against human test sera, an indirect conclusion on the quantity of IgG antibodies in the used sera could be made. Combined tests of 0, A1 and B blood group with erythrocytes treated with formaldehyde against test sera 0 (alpha + beta), A (beta) and B (alpha) and AB (0) sera from non-immunized and immunized with anatoxin from staphylococcus aureus donors were made. The strongest phagocytosis was observed when A1 and B erythrocytes with 0 (alpha + beta) sera and A1 erythrocytes with AB (0) sera from immunized with anatoxin donors were combined. A weaker phagocytosis took place when erythrocytes non-compatible with the AB0-system A1 and B were combined with the B (alpha) and A (beta) test sera, and the weakest--when erythrocytes compatible with the AB0 test sera diluted with an equal volume of saline and heated at 70 degree C for 10 minutes.