Abstract: We studied, through field survey, field inoculation experiments and hand inoculation experiments, whether Geranium sylvaticum plants differed in resistance against a macrocyclic pathogenic rust, Uromyces geranii, when they were healthy or diseased by one of two microcyclic pathogenic rusts, Puccinia leveillei and P. morthieri, and whether the macrocyclic rust interacted with the two microcyclic rusts when they infected the same host plants at the same season. The results indicated that P. morthieri diseased plants were much more resistant to U. geranii than P. leveillei-diseased plants and healthy plants. Furthermore, P. leveillei-diseased plants were more resistant than healthy plants. The results suggest that P. leveillei induces a short-term resistance, while P. morthieri induces a long-term resistance. Induced protective resistance may be one important factor in explaining disease patterns in natural plant populations.