The prevalence of work-related asthma, rhinitis and urticaria was measured in a scientific establishment working with locusts. Twenty-six percent of those handling the locust in the research centre had work-related wheeze or breathlessness, and one-third had work-related rhinitis and urticaria. Work-related symptoms were uncommon in scientists exposed to locusts in the field, and in other employees at the centre. Antigens were prepared from the locusts, Schistocerca gregaria and Locusta migratoria, as well as the moth, Chilo partellus, which was also bred at the centre. Skin prick testing with the locust antigens showed positive reactions in 55% of the atopic workers at the centre, but were also present in 43% of unexposed atopic workers. In this latter group there was a correlation between positive reaction to locust and dermatophagoides antigens. Atopic workers handling the locusts developed occupational asthma more often and more quickly than similarly exposed non-atopic workers. IgG and IgE antibodies to the locust antigens were found to correlate significantly with both the degree of exposure and the presence of disease.