Mutual effects of the spores of Puccinia recondita and its hyperparasite, Eudarluca caricis, have been studied in the infection court of wheat leaves. Eudarluca caricis (Fr.) O. Erikss. (anamorph Darluca filum (Biv.-Bern. : Fr.) Cast., ≡ Sphaerellopsis filum (Biv.-Bern.: Fr.) Sutton) is a hyperparasite of hundreds of rust species ( Kranz & Brandenburger, 1981) including Puccinia recondita Rob. & Desm. We studied the interaction between the latter rust fungus and its parasite on wheat leaves in order to test the effect of urediniospores on germination of E. caricis conidia and vice versa. Further, we wanted to resolve some contradictions in the literature. According to v. Schroeder & Hassebrauk (1957) and Carling, Brown & Milikan (1976), E. caricis penetrates urediniospores, but Arsenijevic & Kostic (1967) and Rambo & Bean (1970) were not able to observe this.