Additional family data support the hypothesis of autosomal codominant inheritance of alleles Pb 1and Pb 2that determine the parotid basic protein (Pb) polymorphism in Blacks. These highly basic, low molecular weight proteins have thus far been found only in the saliva. The multibanded patterns as well as variations in band intensity and mobility in the phenotypes may be determined in large part by proteolytic degradation occurring in the parotid gland. A set of four Pb proteins similar in appearance but with somewhat slower mobility compared to that in man is present in three Old World monkey species of the genus Macaca, M. mulatta, M. speciosa, and M. nemestrina, but not in the New World monkey Saimiri sciurea, the dog, or the rat. There are slight differences in the mobilities of the bands among the macaque species, but genetic polymorphism was not found in a limited sample. It is postulated that these basic salivary proteins may have been close to their present form for over 50 million years.