Tiacrilast is a potent mast cell degranulation inhibitor in vitro and in animal studies. Since mast cells and their mediators are possibly involved in atopic eczema, we have studied a topically applied 3% hydrogel formulation of tiacrilast against vehicle in a multicenter, double-blind, placebo-controlled trial. Drug or vehicle were applied on involved skin for 28 days. Efficacy was assessed weekly using a 4-point scale for erythema, scaling, induration, exudation and pruritus. An overall assessment of the sites for efficacy and site preference was performed at the end of treatment. In the 32 patients evaluable for efficacy, > 33% improvement was noted on 78% of the drug- and 75% of the vehicle-treated sites, with no statistically significant differences for any of the parameters tested. Treatment was generally well tolerated by all patients. These data suggest that mast cells may not play a major role in the maintenance of atopic eczema lesions.