There was a reduced prevalence of symptoms of Extrinsic Allergic Alveolitis (EAA) among the cigarette smokers in a survey of 102 volunteer pigeon breeders. These smokers had a significantly lower antibody response against the inhaled antigens associated with the disease; only one of twenty-three smokers (4.3%), but thirty-nine of sixty-five non-smokers (55.4%) had elevated serum IgG antibody levels, despite similar degrees of avian exposure in each group. The appearance of antibody in six of fourteen ex-smokers (42.9%) suggested that the apparent inhibitory effect of smoking on the antibody response was reversible. The smoking group had lower total serum IgG and IgA, higher serum IgD, and their total IgM and IgE levels were similar to the non-smokers.