From the plant Schefflera arboricola, which has been reported to cause allergic contact dermatitis, we have isolated and determined the elicitor of allergic contact dermatitis as falcarinol, heptadeca-1,9(Z)-diene-4,6-diyne-3-ol. Three polyacetylenes closely related to falcarinol, namely falcarindiol, falcarinone and dehydrofalcarinone were tested simultaneously. Falcarinol, but not falcarindiol, falcarinone and dehydrofalcarinone, elicited allergic contact dermatitis in a 38-year-old female plant-nursery worker.