Between April 4 and May 10, 1982, fifty-four individuals developed a poison ivy-like dermatitis 1 to 8 days after eating imported cashew nuts. The patients had a very pruritic, erythematous, maculopapular eruption that was accentuated in the flexural areas of the body. Three had blistering of the mouth and four had rectal itching. Nineteen volunteers (eleven ill and eight well) were patch-tested with 2.5 micrograms of poison ivy urushiol and an acetone extract of cashew nut shells. Patch testing did not predict illness since positive tests to both materials occurred in those who had been ill as well as in those who had been well. Absence of cashew nut shells from two thirds of the bags probably accounted for the lack of correlation between patch testing and illness. All nine who reacted to the cashew extract also reacted to poison ivy urushiol. The three who were not sensitive to poison ivy had no reaction to cashew extract. Mass spectrometry of the cashew shell extract suggested the presence of cardol , one of the allergens in cashew shell oil.