The first part of the paper outlines the actual situation of the recent investigations on the interpretative problem of the immunological deficits combined with enzymatic deficits. ADA deficit associated with combined immunodeficiency is an autosomal recessive form. Low enzyme levels, which is produced by a structural gene located on chromosome 20, were detected in chronic lymphatic leukemias where ADA decrease is correlated to low levels of T lymphocytes and the prevalence of an atypical B lymphocyte population. Particularly high levels of ADA were detected in acute lymphoblastic leukemias, in transplant rejection, in blastic crisis of chronic myeloid leukemia... NP deficit is associated with a T branch immunodeficiency, with high levels of inosine, guanosine, hypouricemia, hypochromic microcythemia and hematopoietic tissue megaloblastosis. This enzyme, with trimeric structure, whose structural gene is located on chromosome 14, shows a cytoplasmic location, and its maximum activity is to be found in T lymphocytes separated by rosetting. IGPT deficit is to be held responsible for the neurological Lesch-Nyhan syndrome. This deficit is associated with a depression of B lymphocyte function evaluated as response to the mitogens (PWM, Protein A) or as specific immunoglobulins production. At last the Authors report some personal investigations performed on hemolysates and lymphocytes of subjects with impaired immunity, as well as on some children at birth to establish the correlation between ADA and NP behaviour and immunosurveillance. Lastly, the data on the variations of the enzymatic and immunological parameters of subjects with immunodeficiency associated to enzymopenia after red cell transfusion are reported.