The following blood group phenotypes and antigens were studied: Abantu , Ax, Ay, Bm, Bm-like, B3-like, "Bombay" Oh Le(a+b-), "Bombay" Oh Le(a-b-), para-Bombay, Mi(a+), Vw+, S-s-U-, Dantu, Gerbich-, P1H, STEM+, Rh :-34, Rhnu11 , Le(a-b-c-d-), McC(e+) and Wd( a+) and a new form of polyagglutination associated with haemoglobin M - type Hyde Park. The effect of inheriting a y, D--, Dc- or R1Lisa haplotype was also investigated. The following blood group antibodies were studied: anti-N in a person with type MN red cells, anti-hrs, anti-Rh34, anti-Jsb and anti-T. Type M red cells were confirmed to absorb anti-N and type N red cells not to absorb anti-M. A new technique was described for separating the two red cell populations in twin chimeras. Three XX/XX female dispermic chimeras with blood of two genetic types, two with patchy skin pigmentation, were identified. Reduced I and enhanced i antigen expression helped confirm a case of congenital dyserythropoietic anaemia type II. Oval red cells accompanying an r (dce) haplotype were found, and anti-Tja-like haemolysins were not detected in women about to abort. Aspects of haemolytic disease of the newborn due to ABO and Rh antibodies were discussed. Two new tests in which 2-mercaptoethanol was used to distinguish between IgG (7S) and IgM (19S) immunoglobulins were described. Blood group phenotype and gene frequency studies were made in Black, White, Indian and Coloured blood donors and the results were presented in 32 tables. Thirty monoclonal anti-A and 96 monoclonal antibodies for antigens in the ABO, MNSs, Rh, Lutheran, Kell, Lewis and Kidd systems and for other antigens were investigated for their activity and specificity. / Thesis (Ph.D.)-University of Natal, Durban, 1991.