Skin areas of 10X10 cm were marked out and closely observed during 14 days in 22 patients with active and 18 cases with less active psoriasis. The first changes - minute papules, slightly erythematous, almost flush with the skin (pre-pin-point papules) appeared within this period and transformed after several days into pin-point lesions. Histological examinations performed in 25 pre-pin-point and 10 pin-point papules, as well as cytochemical studies have shown significant differences. In the pre-pin-point papules inflammatory infiltrates were in a great part polymorphonuclear, and the epidermis had no features characteristic of psoriasis. The performed studies have shown that the earliest changes preceding the appearance of spontaneous psoriatic papules are very much like those of provoked Koebner phenomenon.