The effect of cyclosporin A (CSA) on the elicitation phase of allergic contact dermatitis was investigated. Initially, the ability of CSA to penetrate normal human cadaver skin was determined using 3 different vehicles. 10% CSA in Labrafil was found to be the most effective combination at achieving skin penetration (0.33%). Patients with known contact sensitivities to a variety of allergens were selected. After a 48-h pretreatment with 10% CSA in Labrafil, skin sites were exposed to the appropriate contact allergen. 72 h later, the development of an eczematous patch test reaction was evaluated. Only 1 of 10 patients showed unequivocal signs of suppression of allergic contact dermatitis.