The polymorphism of glyoxalase I was investigated in 169 mother-child combinations from southwestern Germany. Glyoxalase I (GLO) has 3 common phenotypes: GLO 1, GLO 2-1, and GLO 2. The results are in good agreement with the formal hypothesis: Two alleles GLO1 and GLO2 at an autosomal locus. The GLO1 gene frequency was estimated to be 0.39. From the electrophoretic pattern the GLO-molecule appears to consist of two subunits.