Twenty-three patients with extrinsic allergic alveolitis due to an allergy to inhaled budgerigar serum protein (budgerigar fancier's lung disease) were typed for HLA-A, B, C and HLA-DR antigens. Antigen frequencies were compared with those found in 154 healthy control subjects. No statistically significant variation in the frequency of any HLA antigen was detected. Exclusion of two patients who had concurrent coeliac disease, and subdivision of the population into those with acute and chronic disease, failed to reveal any significant association with an HLA specificity. A non-significant increase in B8-DR3 amongst the patients with acute disease was noted. Possible reasons for the apparent HLA associations previously reported by others for extrinsic allergic alveolitis are discussed.