Serologic experiments are described in which was studied the agglutination of leukocytes from donors representing various ABO, Rh, and Lewis erythrocyte groups an certain canine blood groups, in the presence of corresponding antisera.

Appropriate mixing of antisera with leukocytes and erythrocytes from donors of different groups was seen to produce clumping of leukocytes which did not conform to the reactions of the erythrocytes from the leukocyte donor. When viewed under phase microscopy, certain of these leukocyte clumps, which appeared homogeneous with ordinary light microscopy were found to be clumps of leukocytes mixed with ghosts of erythrocytes reacting with the antibody present.

Factors contributing to this apparently immunologically non-specific clumping were the presence of complement-fixing, potentially hemolytic antibody and thermolabile components of serum. A possible relationship with erythrophagocytosis is suggested.

These observations indicate that certain results of this and other "leukoagglutination" technics, which have been interpreted as demonstrating the presence of A and B antigens on human leukocytes, deserve re-evaluation and emphasize the importance of developing methods of preparing homogeneous leukocyte suspensions.

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