Phytophotodermatitis from Heracleum laciniatum is described in 2 typical cases. Experimental phytophotodermatitis was produced using homogenates from leaves of the plant and long-wave ultraviolet light. The homogenates of leaves produced strong phototoxic reactions. The minimal phototoxic erythema dose was determined to be lowest for abdominal and midback skin. The action spectrum for Heracleum laciniatum homogenates applied topically was found to be in the range 315-375 nm with peak sensitivity at 330-335 nm.