For DII and DIVa, RHD antigen sites per cell were tested previously only with a limited number of radio labelled anti-D. We determined RHD antigen densities (sites/cell) by flow cytometry with 64 anti-D in four partial RHD red cells. Epitope densities detected (mean +/- SD) were: DVII 8,000 +/- 1,665 (number of anti-D used for calculation: n = 55; percentage of reference cells: 47%); DNU (DIIlike) 6,869 +/- 1,381 (n = 47; 29%); and DHMii 20,626 +/- 4,320 (n = 55; 87%). One DIV cell revealed two peaks with a low fluorescence range of 18,158 +/- 2,504 (n = 11; 76%) and a high range of 35,477 +/- 2,485 (n = 6; 149%). We established epitope density profiles with a large panel of anti-D for four RHD variant cells and determined the number of RHD antigens per cell.