The authors research 3029 people of the both sexes living in South Western region of Balkan's peninsula according to their blood group systems ABO and Rhesus belongings. The observed people are divided in 5 nationalities Montenegros, Vlahs, Macedonians, Greeks and Albanians. The statistical analysis by standard shows that there are significant differences in blood group system's distribution (K=16, p<0,001, γ2= 41,6908) so as in Rhesus factor's (K=4, p<0,001, γ2= 22,9656). These results are based specialty to predominance frequency of the blood group 0 in Greeks and Albanians and a lower percentage of the negative Rhesus factor in Vlahs (6.39%) and Greeks (9.71%).
