The clinical assessment of patients with plaque-type psoriasis is performed by open, intrapatient comparison of 0.2% STA-21 with vehicle(Vaseline) alone within a 2 week period.

Two discrete psoriatic lesions with a similar size (approximately coin-sized) and clinical severity are selected in each patient. Clinical assessment of psoriatic lesion severity is performed at the baseline and at 1 and 2 (end of treatment) using the scores of erythema, induration, scaling on a scale of 0-4 by two observers. Since STA-21 inhibits Stat3 activation, which is essential for disease activity of psoriasis, topical application of 0.2% STA-21 in Vaseline should improve psoriasis in two weeks.

Inclusion Criteria:

• A history of plaque psoriasis for a minimum of 2 years.
• In good general health, as evidenced by blood, renal function, and liver function tests conducted before commencing the study.
• Patients of childbearing age who agreed to continue using birth control for the duration of the study.
• Men or women between 20 and 80 years old.

Exclusion Criteria:

• Chronic plaque psoriasis involving >40% of the body surface.
• Pustular or generalized erythrodermic psoriasis.
• Use of medications that might affect the psoriasis during the study
• Systemic therapy for psoriasis within 60 d of baseline.
• UV therapy within 21 d of baseline.
• Topical therapy within 14 d of baseline.
• Positive for HIV, hepatitis B, or hepatitis C.
• Clinically significant laboratory abnormality in blood, renal function, or liver function.
• Lactating, pregnant, or planning to become pregnant.
• Participation in another clinical trial in the last 30 d.
• Unwillingness to comply with the study protocol.
• Any other condition that in the opinion of the investigators could compromise the study.