A new antibody that reacts with all human bloods except those of type Fy(a-b-) has been named anti-Fy3. It is believed to detect a previously unknown bloodgroup antigen, which is possibly a precursor of Fy& and Fyb. Key Words Duffy blood groups New antibodyFollowing discoveries by CUTBUSH, MOLLISON and PARKIN [3] and by IKIN, MOURANT, PETTENKOFER and BLUMENTHAL [4], the Duffy blood groups were established as a system involving two antigens, Fya and Fyb, identified b y two antibodies, anti-Fya and anti-Fyb. The existence of Fy, allelic to the genes Fya and Fyb, was postulated by SANGER, RACE and JACK [8] t o explain the occurrence of the