A large group of glucocorticosteroid formulations were assayed by the vasoconstriction test in normal skin sites and paired comparison studies in patients with psoriasis. Excellent correlation between the vasoconstriction assay and selected paired comparison studies occurred in 20 of 23 instances. In three instances, involving two glucocorticosteroid formulations tested, correlation was absent. The vasoconstrictor assay is an inexpensive and reliable method for screening glucocorticosteroid formulations for clinical activity in psoriasis.