With the aid of Eldon cards the distribution of the ABO blood groups and of the Rh factor (D) was investigated in different native ethnic groups (Kafirs, Kalash, Chitrali) in the Hindu Kush region of Afghanistan and Pakistan. All studied groups are characterized by a relatively high frequency of blood group gene A and extremely low frequencies of B and O. This distribution differs appreciably from that of the rest of the Indian subcontinent as well as that of the adjacent Central Asiatic areas. The possible causes of the exceptional position of the native Hindu Kush groups in the ABO blood group system are discussed. It may be assumed that selection as a result of mother-child compatibility played a role as will be shown in a later paper. Concerning the studied traits of the Rhesus system, all investigated groups fit in the range of variation of the South Asian area.