The classical division of the immune reactions into an immediate humoral type and a cellular late type is left in favour of a classification in 4 forms of reaction according to Gell and Coombs. This classification allows of a by far more reasonable coordination of the diagnostic measures as well as aimed therapeutic conclusions. In detail are differed: type I as anaphylaxis and reagin type (mediator-substance-type), example-anaphylactic shock and asthma; type II as cytotoxic type (cytotoxic antibodies), example-Coombs-positive haemolytic anaemia; type III as immune complex type, examples-serum disease, Arthus-reaction, glomerulonephritis; type IV as type of the cellular immune reactions. Combinations and transitions are possible in the same way as a further sub-classification of the types. It is demonstrated as by the combination of in-vitro-tests, skin tests and, perhaps, bioptic investigations the type is to be determined as far as possible. Only this allows an aimed and reasonable therapy.