Direct immunofluorescent microscopy was positive on skin biopsy specimens in thirty-one of sixty patients with various forms of psoriasis. Patients with positive immunofluoreseence were classified into five main clinical subgroups: (1) psoriasis vulgaris with decreased tolerance to sunlight or ultraviolet light B (eight patients), (2) psoriatic arthritis (seven patients), (3) guttate psoriasis (five patients), (4) pustular psoriasis (four patients), and (5) “uncomplicated” psoriasis vulgaris (seven patients). Various patterns of deposition of immunoglobulins, complement, and fibrin were seen in the five subgroups, the most consistent being granular C3 at the basement membrane zone in specimens from five of the seven patients with guttate psoriasis. Direct immunofluorescent microscopy was usually negative in psoriasis vulgaris, but positive results may be anticipated in special forms of psoriasis.