The formal genetics of the ADA polymorphism had been investigated in a series of 156 German families with 319 children. The results correspond to the formal model of two alleles at an autosomal locus. There is no evidence for close linkage between the loci of ADA and ABO, MNS, Kell, P, Duffy, Rhesus, Haptoglobin, Gc, ac. Phosphatase, AK, PGM1, 6-PGD. © 1969 Springer-Verlag.