Chronic bronchial suppuration has been associated with elevations in immunoglobulin levels, circulating autoantibodies and immune complexes but the cause is obscure. In order to investigate one possible explanation we studied eight male subjects (mean age 54.9 years, range 39-68) and 16 female subjects (mean age 45.2 years, range 24-68) with bronchial suppuration attributed to bronchiectasis. Gram-negative organisms were found in the sputum of 95% of subjects. Forty per cent (10 subjects) had elevations in immunoglobulin levels and 60% (15 subjects) had circulating autoantibodies. Eighty-eight per cent (21 subjects) had mild-moderate increases in the level of C-reactive protein. Endotoxin was detected using the limulus amoebocyte lysate test in 50% (12 subjects). Endotoxin was found only in patients with an immunological abnormality and was more likely to be detected in those with both elevated immunoglobulins and circulatory autoantibodies. It is suggested that the endotoxin may be of aetiological significance in the development of autoantibodies and elevations of immunoglobulin levels.