Between December 1989 and June 1990, 1,874 reports of alleged malathion application related illness from repeated spraying of a mixture of malathion corn syrup bait to eradicate a Mediterranean fruit fly infestation in Southern California were received by the Toxics Epidemiology Program of Los Angeles County. Among these complaints were 47 reports of urticaria, 38 reports of angioedema and 213 reports of a nonspecific skin rash. In order to determine whether these alleged skin reactions were the result of an immediate or delayed type of hypersensitivity reaction to malathion or to the corn syrup bait we studied ten subjects referred for testing by the local health department. All ten subjects had no reaction on patch testing. One child exhibited a positive reaction to the bait and one child had irritant reactions to malathion and to the bait. This study documented one case of a possible immediate IgE reaction to malathion bait. Due to the low participation rates in this study, no specific conclusions concerning the rate of sensitivity in the population can be drawn, although it appears that such reactions are uncommon.