Oilseed rape (Brassica napus) is a commonly grown crop in Europe and it has been suggested that its pollen may be a potent new allergen. The prevalence of sensitization in a normal exposed population and an objective study of those patients found to be allergic to the rape pollen is described. The results show a low prevalence of allergy to oilseed rape pollen (less than 0.2%) unless the subjects were occupationally exposed. Those affected, with one exception, were already atopic and allergic to other pollens. The role of volatile materials given off by the plant remains to be elucidated.