The buttercup is an inportant irritant plant which contairs an unsaturated lactone, protoanemonin, formed by the breakdown of a glucoside in injured plants. We report the three cases of irritant contact dermatitis due to buttercup(Ranunculus sceleratus). These patient developed erythematous and edematous patches with tense vesicles or bullae on t,he application site of pounded buttercup for the treatment of diabetes mellitus, arthralgia, and neuralgia, respectively. (Kor J Dermatol .992;30(S):886-891)