Soon after the elucidation of the role of IgE 40 years ago it was suggested that helminthic infections might promote the development of clinical allergies. Later, evidence emerged that such infection might inhibit allergies. Antihelmintic treatment programmes for children in tropical areas are regarded as a high priority but there is concern that they might be followed by an increase in the prevalence of allergic diseases. Now a study in Ecuador ( Lancet2006;367:1598–603OpenUrlCrossRefPubMedWeb of Science; see also Comment, ibid: 1556–8) has provided some reassurance. A total of 2373 children (mean age 9 years) in 68 rural schools were randomised by school to treatment with albendazole (400 mg every 2 months for seven doses) or no treatment. Over the course of the trial geohelminth prevalence fell from 69% to 21% in the treatment group and from 75% to 67% in the control group. There was no increase in prevalence of atopy, as judged by skin-test reactivity to mixed mite extract, cockroach, or grass pollens, in the treatment group. During the course of the study 3% of children in each group wheezed and there were no differences between the groups in any other manifestations of clinical allergy. It is concluded that intensive programmes of deworming in endemic areas are unlikely to give rise to an increase in allergy, at …