Using gene frequency data for 62 protein loci and 23 blood group loci, we studied the genetic relationship of the three major races of man, Caucasoid, Negroid, and Mongoloid. Genetic distance data indicate that Caucasoid and Mongoloid are somewhat closer to each other than to Negroid. Analysis of restriction site data for mitochondrial DNA also shows the same genetic relationship. It seems that the Negroid and the Caucasoid-Mongoloid groups diverged about 110,000 +/- 34,000 years ago, whereas Caucasoid and Mongoloid diverged about 41,000 +/- 15,000 years ago. The genetic relationships of various races in each group of Caucasoid, Negroid, and Mongoloid were also studied. All European populations are genetically close to one another except the Lapps, whereas many African, Oceanian, and Amer-indian tribes show large extents of genetic differentiation. The major cause for this differentiation seems to be the bottleneck effect. The Polynesians, Micronesians, and Indonesians are more closely related to the Asian Mongoloids than to the Australoids in Australia and New Guinea. There are also indications that migration played an important role in forming the current genetic relationships among human races. The extent of genetic differentiation between human races is not always correlated with the degree of morphologic differentiation. The genetic differentiation at protein loci seems to occur largely by mutation, genetic drift, and isolation, whereas morphologic characters are apparently subject to stronger natural selection than "average protein loci."