Generally speaking, we can say that the incidence of certain diseases in the various blood groups of the ABO system do not demonstrate a direct connection which might be used for the assessment of life expectancy, but that exogenic and genetic factors form a genetically determined functional unity in the development of certain characteristic features and of diseases. Innumerable influences of various types can cause diseases, primarily the high incidence of certain tumours in old age, climatic influences, overeating and malnutrition, furthermore abuse of coffee, tea, tobacco and alcohol, medicines and insufficient movement. It can be assumed that wherever blood group A is prevailing the genes of blood group A constitute a factor in the respective polygenic system. The impact of the blood group genes varies as a function of the underlying disease, the effectiveness of the exogenic factors and the general constitution of the individual patient.