Three new cytotoxicH-2specificities are defined. H-2.37 is present in allelesf, p, andpa;H-2.38 in allelesp, pa, andw;and H-2.39 in allelesb, f, andi.The first two specificities have appeared in a number of antisera and, in every case, were without hemagglutinating activity. H-2.39 was very weakly hemagglutinating in one antiserum, nonhemagglutinating in another. The presence of 39 in alleleband the crossover-derivediand its absence from crossoverhplaces 39 at the K end (although not necessarily in the K region) of theH-2crossover map.