Forty-eight budgerigar fanciers have been studied and twenty-five (52%) of these lost their serum budgerigar precipitins after cessation of avian exposure. Twenty (80%) subjects lost their precipitins within 2 years. The lung function was assessed serially in seventeen patients with allergic alveolitis and correlated with the persistence of their serum precipitins. There was no difference in the lung function at presentation or in the incidence of complete recovery between the ten subjects, whose precipitins persisted for longer than 2 years, and the seven individuals in whom the precipitins had disappeared within this time. These observations suggest that budgerigar precipitins do not have a major role to play in the continuing pathogenesis of allergic alveolitis.