The Duffy (FY) blood group system is clinically significant in transfusion medicine because FY antibodies are involved in hemolytic transfusion reactions and hemolytic disease of the newborn. The Fy(a) and Fy(b) antigens are encoded by the FY*A and FY*B alleles which are responsible for the Fy(a+b+), Fy(a+b-) and Fy(a-b+) phenotypes. The Fy(a-b-) phenotype is found in individuals homozygous for a silent FY*B allele, named FY*B ( ES ), which is caused by a mutation in the promoter region of FY*B that result in the loss of FY expression in the erythroid linage. The aim of the present study was to evaluate the role of FY DNA typing as a tool in transfusion compatibility testing. We studied 275 white blood donors from the city of Rosario by serological method and allele specific PCRs. We found that the 106 serologically Fy(a+b+) samples all genotyped as FY*A/FY*B (100%). Among the 94 Fy(a+b-) samples, 81 (86.2%) were FY*A/FY*A and 13 (13.8%) were FY*A/FY*B ( ES ) . Of the 75 Fy(a-b+) 67 (89.3%) were FY*B/FY*B and 8 (10.7%) were FY*B/FY*B ( ES ). No Fy(a-b-) samples were encountered. The frequencies of the FY*A, FY*B and FY*B ( ES ) alleles clearly revealed that the genetic pool analyzed is comprised of Caucasian and non-Caucasian alleles. These results showed that there is an important proportion of patients phenotyped as Fy(b-) that can be exposed to Fy(b+) blood units with no risk of alloimmunization when they carry the FY*A/FY*B ( ES ) genotype. Thus, FY genotyping allow increasing the pool of compatible units facilitating transfusion therapy and benefiting patients that require chronic transfusions.