Abstract: The plasma fibronectin(Fn) level was determined by immuno-diffusion in 35 normal persons, 58 cases of psoriasis and 13 patients with other skin diseases. It was shown that plasma Fn level increased in the patients with psoriasis, especially in the active cases and the patients with long duration. It was considered that the increased plasma Fn was a regulation reaction against the abnormal proliferation and differentiation of kerationocytes. In the paper, the distribution of Fn was observed by IIF in the skin specimens from 10 normal persons and skin lesions from 8 patients with psoriasis. The results showed that in the lesions of psoriasis the Fn was found within the epidermis whereas the Fn was negative in the normal skin. It is the author's opinion that the Fn in the epidermis of the psoriatic lesion may be come from the plasma.