This paper reviews our modification of the vasoconstrictor (blanching) assay for topical corticosteroids using human volunteers, which we have improved and extended so that it may be used as a useful screening test for clinical efficacy besides being employed to determine the bioavailability of steroids from topical bases. Work is reported on the blanching activities of (1) 14 novel steroids in ethanol, (2) hydrocortisone 17-butyrate in eight topical vehicles, (3) betamethasone 17-benzoate in foam, ointment, cream and gel bases, and (4) 61 commercial formulations used in Great Britain. Pharmacokinetic/pharmacodynamic relationships are discussed as aids to optimizing topical steroid treatment.