Siegler, D. I. M. and Citron, K. M. (1974).Thorax, 29, 313-316. Serum and parotid salivary IgA in chronic bronchitis and asthma. It has been suggested that immunoglobulin A (IgA) deficiency may be an important predisposing factor to infection in chronic bronchitis and that this occurs more often in extrinsic asthmatics than in normal subjects. These claims have been investigated by measurement of IgA in stimulated parotid saliva and serum in chronic bronchitics and asthmatics. Salivary and serum IgA levels in 84 chronic bronchitics could not be correlated with sputum purulence, the degree of ventilatory impairment, radiographic evidence of emphysema or the smoking history. Serum IgA was low in 6% and salivary IgA was normal in all cases. IgA levels measured in both serum and saliva in 50 asthmatics showed no correlation with the number of positive skin tests or other evidence of atopy. Serum IgA was low in 8% and salivary IgA was normal in all cases.