To the Editor.—Cornell and Stoughton1reported excellent correlation in 20 of 23 instances between the vasoconstrictor assay for topical corticosteroid preparations (16 hours [57 600 s] nonoccluded application, single reading measurement) and paired comparison studies in psoriatic patients. Among those not demonstrating equivalence was 0.2% hydrocortisone valerate cream compared with 0.1% betamethasone valerate cream. No difference between the preparations could be detected clinically, but hydrocortisone valerate cream was superior in the skin blanching test.Gibson2stated that he found the best correlation between the vasoconstrictor assay and clinical efficacy in psoriasis using a modified skin blanching technique (six hours [21 600 s] occluded application, serial readings between seven hours [25 200 s]and 25 hours [90 000 s], followed by analysis of the areaunder-the-curve values produced). Stoughton and Cornell3replied that it would be very interesting to examine hydrocortisone valerate cream using an area-under-the-curve method.