Absorption studies were performed to analyse the properties of heterophile antibodies in Japanese sera. The conventional absorption test using ox erythrocytes and guinea pig kidney tissues classified 28 of 3570 pathologic sera and 12 of 19 IM-like syndrome sera into 2 categories of Forssman type and Hanganutziu Deicher type. No sera contained the antibody of Paul-Bunnell type. Absorptions of the representative sera with cells of various species disclosed the presence of Hanganutziu Deicher-like and Forssman-like antibodies in Japanese IM-like syndrome sera. The activity of both antibodies were removed partly or non-significantly with rat cells. The antibody properties in serum sickness serum between Japanese and a Caucasian were compared. Cells of ox, rabbit, guinea peg and mouse removed the antibody in Japanese sera, however, rabbit cells did not absorb it in a Caucasian case. It could be proposed that various cells other than ox and guinea pig should be employed in the absorption study of the heterophile antibodies.