The examination of induced Koebner reactions in 71 patients by the IF methods and by histology at selected times after scratching, show, that immunologically specific but non-disease specific reactions of stratum corneum (SC) antibodies occur adjacent to the crusts in both control subjects and psoriasis patients. In lesions induced by scratching in patients with psoriasis there develop progressively additional foci of apparent in viveo binding of SC antibodies. IF deposits may appear before histologic or clinical changes. The widespread immune deposits in the SC with typical histologic changes of psoriasis seem to be a sign of impending clinical psoriasis while single foci of in vivo bound SC antibodies may be cleared by the body without the development of psoriasis.