Iranian Jews represent a very ancient Jewish community with a high frequency of inbreeding. A sample of Iranian Jews, mainly unrelated students, was tested for genetic markers of red blood cells and serum. The frequency of glucose-6-phosphate dehydrogenase deficiency was not uniform among Jews who had lived in different areas of Iran; it was lower among those from central Iran (6.7%) than in those from southern and western Iran (16.7% and 20.6%, respectively). The frequencies of B, CDe, cDE, S, and K alleles were among the highest recorded in Jewish ethnic groups. Iranian Jews were similar to Iraqi Jews with respect to the frequencies of the blood markers B, CDe, cde, cDe, ACP, PGM1, ADA, and Hp; however, the B and CDe markers occur with similar frequencies among indigenous Iranians. The presence of the cDe allele and the Gm1,5,13,14,17 haplotype in low frequencies indicates black admixture. Mongoloid admixture is indicated by the polymorphism of the Gm1,13,15,16,17 haplotype. The very rare phenotype Gm(3,5,13,14,17) was observed in 4.8% of 167 individuals tested. This phenotype has not been previously observed among Jews.