[Immunological reactivity of the host as an environmental factor and its significance for the development of parasitism].

Concepts--mainly of SPRENT (1959, 1963), DINEEN (1963) and DAMIAN (1964)--concerning the immunological aspects of the phylogeny of host-parasite associations and the function of immune processes in the host-parasite relationship are discussed. In the light of some recent findings an integrating interpretation of the available body of evidence is attempted. The significance of the immuno-selection pressure during the course of host-parasite coevolution is stressed and some of the consequences of this pressure seen in the existing host-parasite systems are pointed out.