Glucocorticoid-induced dermal blanching provides a useful research tool to study steroid potency and sensitivity. Conventional measurement of the intensity of blanching relies on subjective assessment by a trained observer using a visual score. Several objective techniques have recently been reported to detect skin blanching, but their sensitivity has not been compared previously with subjective visual recordings. In this report we aimed to establish whether objective methods offer sufficient sensitivity to be employed in epidemiological studies of glucocorticoid responsiveness. In healthy subjects we applied beclomethasone dipropionate at three concentrations (1, 10 and 100 micrograms/ml) under an occluded dressing overnight. The following morning we measured blanching using a visual score, laser Doppler velocimetry with the MBF 3D monitor (Moor Instruments Ltd, U.K.) and a perfusion imager (Lisca, Sweden), and reflectance spectrophotometry with the Dia-Stron 'erythemameter'. Using the visual score, blanching was detected at all concentrations of steroid. Neither laser Doppler instrument detected vasoconstriction at any concentration. By contrast, the reflectance spectrophotometer successfully recorded blanching at 10 and 100 micrograms/ml, but not at 1 microgram/ml. We conclude that laser Doppler instruments, including the novel scanning perfusion imager, do not detect glucocorticoid-induced skin blanching, perhaps because it reflects venular rather than arteriolar vasoconstriction. By contrast, the Dia-Stron reflectance spectrophotometer has sufficient sensitivity to be used as an alternative to visual assessment in epidemiological studies of human glucocorticoid-induced dermal blanching.