Introduction All years that are important for the development of the transfusion medicine such as: the development of bood types, Rhesus factor, Coombs test and so on have been given at the begining of the introduction . The following text contains definitions of the erythrocyte antigens, their structures and functions in the human body. The erythroctye membrane of a newborn isn't fully developed until the sixth month of life, so based on that the anti-erythrocyte antibodies can firstly be detected in the serum after six months of life. Inheritance of a certain blood type follows the Mendelian law of inheritance and it consists of synthesis of a certain gene or a group of homologous genes. Alleles A and B are co-dominant and the allel 0 is recessive. Rh factor analysis as well as Coombs tests are preformed with the blood typing simultaneously. There are two types of a Coombs test, the direct and the indirect one which will be disscussed later in the Chapter 3.2. Knowing your Rh factor is very important during pregnancy. If the mother is Rh negative and the child has inherited Rh postive factor from the father the fetus has a chance of developing a fatal hemolythic disease of the newborn. Objective The objective of this assay is to highlight the importance of Sources of information and methods There are certain rules and protocols that have to be followed in each labaratory when a immunohematology testing is being preformed. Venous blood mixed with anticoagulant EDTA in a test tube is used as a sample. There is a prescribed list of reagents that should be used including: ortho biovue cassettes, 0.9 % saline solution of sodium chloride, reagents for hemotests for test tubes and plates, reagents for detection of weak Rh (D) antigene, low ione strength Bio-LISS solution, Diluent 2 solution and test erythrocytes. Recomended instruments, that have been previously validated, should be used in alignment with the correct reagents and with the correct labaratory equipment which consists of: test tubes, micropipettes ,micropipettes tips and holders. Discussion In the discussion a case of a pregnant woman with O- blood type carring a Rh(D) + child who was diagnosed A+ blood type after birth is shown. Conclusion Correct handling and interpretation of immunohaematological testing of the mother and her newborn is vital in preventing ABO/Rh(D) immunisation. Every pregnant woman must be tested and further controls will depend on her Rh(D) blood type. A sense of responsability must be shown by every pregnant woman during her pregnancy in order to insure that she and her child get the best medical care possible.