Some chironomid (non-biting) midges contain potent human allergens, principally in the form of insect haemoglobins. In view of previously demonstrated immunological cross-reactivity between some different midge species, the possible role of British midges in allergic disease was studied. The chosen site, Farmoor near Oxford, is a village that has been subject to several annual nuisance midge swarms since the construction of an adjacent water-supply reservoir in 1964, which was extended in 1975. The incidence and severity of hypersensitivity in the community was assessed by questionnaire survey, skin-prick testing, radio-allergosorbent tests (RAST) and RAST inhibition, and enzyme-linked immunosorbent assays (ELISA) and ELISA inhibition, using extracts of locally caught adult midges (Tanytarsus sylvaticus, T. bathophilus and Chironomus anthracinus) and laboratory cultured larvae (C. riparius). These tests revealed a low but significant level of midge-related hypersensitivity with skin-prick results showing seasonal fluctuations, but this seasonality was not confirmed with an IgE RAST. A correlation between IgE levels and relevant symptoms was found (P<0.01) using RAST, but not between IgE and skin-test results. Enzyme-linked immunosorbent assay results did not correlate with any other parameter measured. The incidence and severity of allergic reactions to the midges tested in this community was low.