Objective: To determine the in vivo allergenicity of two grades of peanut oil for a large group of subjects with proved allergy to peanuts. Design: Double blind, crossover food challenge with crude peanut oil and refined peanut oil. Setting: Dedicated clinical investigation unit in a university hospital. Subjects: 60 subjects allergic to peanuts; allergy was confirmed by challenge tests. Outcome measures: Allergic reaction to the tested peanut oils Results: None of the 60 subjects reacted to the refined oil; six (10%) reacted to the crude oil. Supervised peanut challenge caused considerably less severe reactions than subjects had reported previously. Conclusions: Crude peanut oil caused allergic reactions in 10% of allergic subjects studied and should continue to be avoided. Refined peanut oil did not pose a risk to any of the subjects. It would be reasonable to recommend a change in labelling to distinguish refined from crude peanut oil.