The biliary excretion of aztreonam was studied in 10 post-cholecystectomy patients with T-tube biliary drainage (group A) and four other subjects with obstructive biliary tract disease who had recent placement of external biliary drainage (group B). Maximum biliary levels ranged from 9.7 to 88.2 micrograms/ml (mean, 42.9 +/- 7.9 micrograms/ml) and occurred 2.4 h after injection of a single 1-g dose intravenously. Peak biliary levels observed in group B patients were approximately one-third those in group A. Cumulative 12-h biliary excretion (group B) accounted for 0.18 +/- 0.06% of the total dose. In the same period, urinary excretion accounted for 65 to 72% of the total dose. The lower biliary levels of aztreonam observed in group B patients relative to those in group A suggest that in patients with total biliary tract obstruction the liver may not recover full secretory capacity, at least within 3 to 7 days after biliary decompression.