The results of 38 HL-A and other antigen matching studies revealed an inverse relationship between the percent of donor-recipient serologic discordance and increases in recipient granulocyte levels 1 h after infusion of donor cells. Selected unrelated, parent, and sibling donors possessing mean percent serologic discordances of 33, 22, and 16, respectively, increased postinfusion granulocyte counts by 10, 46, and 117%, respectively. A mean of 1.58 x 10^10 total granulocytes collected from sibling donors was associated with a significant elevation of recipient levels, as compared to unfavorable results with the infusion of 2.05 x 10^10 and 2.31 x 10^10 total granulocytes harvested from less compatible parent and selected unrelated donors, respectively.