The immunoglobulin A and secretory IgA concentrations were studied in the serum and sputum of patients with chronic bronchitis to determine the effect of active chest infection and inflammation upon the estimation of local IgA production. The sputum/serum albumin ratio was higher during chest infection (5.51; SE+/-1.60x10(-2)) than in the non-infected samples (0.75; SE+/-0.14x10(-2);p less than 0.01) suggesting increased transudation as a result of inflammation. There was a similar increase in sputum/serum IgA during infection from 9.47 (SE+/-1.87)x10(-2) to 41.21 (SE+/-6.92)x10(-2)(p less than 0.01). However, the proportion of IgA locally produced when assessed by conventional techniques was unchanged. There was a significant inverse relationship between the estimated local IgA production of the infected samples and the degree of inflammation (r= -0.972;2p less than 0.001) indicating that inflammation was a major determinant of local IgA production. However, the secretory IgA concentrations of the samples were independent of the degree of inflammation. Furthermore, secretory IgA was found in samples that appeared to have failure of local IgA production using the method of Soutar. Clearer information about local IgA production can be obtained by measuring protein components unique to the bronchial secretions rather than applying correction factors to estimate the contribution of serum components, particularly in the presence of inflammation.