The concentration of secretory immunoglobulin A (IgA) has been measured by the immunodiffusion method in 28 chronic bronchitis patients (group A) and in 11 comparable patients receiving corticosteroid therapy (0.5 mg/kg/day prednisone; group B). The measurements have been taken before and after oral administration of Broncho-Vaxom which is an extract of bacteria that usually cause infection of the respiratory tract. The mean concentration of secretory IgA in the saliva was increased by over 130% after the 10-day administration of the preparation to group A patients. This increase was statistically significant between the 12th and 40th day after the beginning of the treatment (p < 0.001). It fell to initial levels after 1 month in 15 patients (group A2) who received a single treatment course. In 13 patients (group A1) who received a second treatment course, beginning 1 month after termination of the first course, the high concentration of IgA in saliva persisted for at least 3 months. The saliva IgA was increased by over 35% in 11 chronic bronchitis patients (group B) who received corticosteroid therapy. In this group of patients the rise of IgA levels began later than in group A. The IgA fell to initial level after 1 month in 5 patients (group B2) who received a single treatment course. In 6 patients (group B1) who received a second treatment course the high concentration persisted longer. The saliva level of IgA in groups A and A1 was higher than in groups B and B1 (p < 0.05 and p < 0.001, respectively). No differences of IgA in the saliva between groups A2 and B2 were found during the study.