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A peptide difference has been found in the neutral-band (pH 6.4) regions of tryptic digests of human transferrins C and DChi. The peptide has the composition Asp-Ser-Ala-Arg. Therefore, this peptide is proposed as the 2TDChi b peptide, the result of the replacement of histidine by arginine in the Tf C peptide.

Blood specimens from putatively pure Maya and Kekchi Indians in British Honduras; Bribri, Boruca, Cabecar and Terraba in Costa Rica; and San Blas Cuna, Choco and Guaymi in Panama have been tested for haptoglobins, transferrins and hemoglobin types, and the phenotype incidences and frequencies of genes controlling these serum proteins have been reported. Hp1 gene frequencies resemble generally those previously reported for Indians but the frequency of 0.197 for Hp1 among the Bribri of Costa Rica is the lowest re-ported for any aboriginal population in Middle America. The distribution of transferrins varies appreciably among these different popula-tions, the range being similar to those reported for other Middle Ameican tribes (Mat-son et al., '63). Nearly all 1,107 hemolysates tested had only type A hemoglobin. Hemoglobin type AS was found in two of 67 Terraba. These two specimens also tested R2r and R0r respec-tively for Rh genotypes, suggesting foreign admixture, since both R0 and r genes are extremely rare or absent in American Indians. Hemoglobin AS was observed also in five (two of whom were brothers) of 153 Guaymi Indians in Panama. One homozy-gous S type was found also among the Guyami. Two AS were present in 198 Samples of blood from the San Blas Cuna.

Peptide analyses have been carried out for chymotryptic digests of transferrin C and transferrin D(1). There is a difference in one peptide, and amino acid analyses indicate that an aspartic acid residue in transferrin C is replaced probably by a glycine residue in transferrin D(1).

Human transferrin D(1) obtained from an Australian aborigine was found to have the same substitution of glycine for aspartic acid in peptide 1C previously shown in transferrin D(1) from an American Negro. This finding is relevant to formation of distinct Australoid and African populations.