In three members of a family from Darmstadt (Germany) a faster migrating Gc variant has been observed. The variant phenotypes have been examined by routine immunoelectrophoresis (Fig. 1), by immunoelectrophoresis with prolonged separation times and with Gc-monospecific antisera (Fig. 2), by polyacrylamide gel electrophoresis (Fig. 3), and by antigen-antibody crossed electrophoresis (Fig. 4). By antigen-antibody crossed electrophoresis the new Gc variant was clearly distinguishable from the Gc Aborigine and from the Gc Chippewa variant. The variant was named Gc Darmstadt (Gc D). Gc Darmstadt has an electrophoretic migration rate intermediate between Gc Ab and Gc 1. In two sibs the type Gc D-2 was observed, the daughter of one of these sibs had the type Gc D-1. The analysis of several members of this family provided only limited information on the mode of inheritance of Gc Darmstadt (Fig. 5). Gc Darmstadt appears to be determined by a gene GcD which may be allelic to Gc1 and Gc2.