SummarySerum and sputum levels of erythromycin and ampicillin were measured over a 24-hour period after single oral 500 mg doses in 30 patients with chronic bronchial disease. Although the serum level curves were similar for both antibiotics, sputum levels were considerably higher and more prolonged with erythromycin. Three groups of 10 patients were each given a different dosage regimen of erythromycin to see which was the most effective in maintaining high serum and sputum levels. Patients received either 250 mg 5-times at 4-hourly intervals, 250 mg 4-times at 6-hourly intervals, or 500 mg 4-times at 6-hourly intervals, and serum and sputum levels were measured over a 24-hour period. The results showed that similar, significantly higher sputum levels were achieved and maintained with the 500 mg 4-times and the 250 mg 5-times dosage regimens than with the 250 mg 4-times dosage regimen.