Accidental induction of photocontact allergy to Heracleum laciniatum.

: Photocontact allergy to psoralens in Heracleum laciniatum occurred in two persons volunteering for investigations into phototoxicity of plant homogenates and purified psoralens. Photoallergy was noted following the fifth exposure in case 1, and the sixth in case 2. Testing with diluted solutions demonstrated allergy to sphondin, isobergapten and pimpinellin.