SummarySputum and serum levels of erythromycin were investigated in 20 adult patients with bronchial disease after oral administration of 500 mg erythromycin stearate and in 20 healthy volunteers after an intravenous infusion of 500 mg erythromycin lactobionate. For comparison, saliva and serum levels were also investigated in 6 healthy volunteers after an intravenous infusion, and after an oral liquid dose of 500 mg erythromycin ethylsuccinate. In the 6 hours after the first dose of erythromycin stearate, sputum concentrations of between 0.2 and 0.6μg/ml were achieved, sufficient for the elimination of most pathogenic bacteria in acute or chronic bronchitis, and were maintained with 500 mg doses 3-times daily. Intravenous infusion resulted in sputum levels approximately 2 to 3 times higher. In healthy volunteers, peak concentrations in saliva and serum after oral administration were only about 15 % of the peak concentrations after intravenous infusion. The ratio between saliva and serum levels was constant and lower (3:1) inpatients. Similar differences between saliva/serum and sputum/serum ratios were also found in patients with bronchial disease.