Eleven putative LD-1 locus homozygous cell donors were found by MLC tests in non-consanguineous families. Lymphocytes from each of them were used as stimulating typing cells in MLC tests together with responding cells from the other homozygous cell donors and from 45 random unrelated individuals. Four of the stimulating typing cells were found to identify a determinant in non-random association with HL-A7; LD-7a, three other cells typed for a determinant non-randomly associated with HL-A8; LD-8a, and one cell seems to identify LD-W5 in non-random association with W5. Two possible additional LD-1 determinants, LD-oh and LD-om, were less well defined with two of the cells. The combined gene frequency of the five possible LD-1 determinants is approximately 0.45 among Norwegians.