Background -Blood provides an ideal opportunity for the study of human variation without cultural prejudice. The frequency of blood groups differ in different geographical areas but the geographical gradients of A and B genes give an indication that the blood groups are affected by environmental selection. The distribution of blood groups is variable in different parts of India. This distribution varies according to different races, population and geographical conditions. Aim – To study the distribution of ABO blood group in different caste groups in population of Uttar Pradesh. Material and Method- The total of 1842 subjects from the population of Uttar Pradesh were randomly included in the study. Venous sample was collected from the subjects and then Cell grouping and Serum grouping was done. Results - Distributional sequence of blood groups is B>O>A>AB in 1842 subjects belonging to the State of UP is followed by the various caste groups except the Brahmin caste groups which shows the following pattern: O > B > A > AB. Conclusion- Caste system in India was according to hereditary professions and status in society. But this is not true nowadays. People change professions and also leave their hometowns for earning their livelihood. But there is still endogamy observed in the different caste groups. Blood groups being genetically inherited, thus maintain hereditary pattern typical to these caste groups.
Key words: ABO blood group, agglutinins.