Adverse effects caused by airborne material to the respiratory tract are due either to non-specific irritation or to hypersensitivity. In this study 20 people employed in swine barns and 18 controls were tested for sensitisation against dusts present in the barn. Immunoprecipitation and enzyme-linked immunoassay (ELISA) were used to test for IgG antibodies; IgE antibodies against swine epithelium were tested using solid phase radioimmunoassay. Precipitins against swine antigens were found in two swine workers; while ELISA found six to be sensitised. Sensitisation against swine antigens correlated with exposure but not with the presence of symptoms. No IgE antibodies were found. Precipitins against feed antigens were detected in 12 workers; in nine of the 12 with symptoms, and in three of the eight asymptomatic workers. No single antigen was of special importance as an inducer of sensitisation. Sensitisation against feed dusts in barns, as indicated by the presence of circulating antibodies, suggests an immunological background for persistent symptoms. A large antigen penal should be used in testing for sensitisation because of the many immunogenic dusts present in the air in swine barns.