Background. The recommended treatment for traveler's diarrhea is the combination of an appropriate antibiotic (usually a fluoroquinolone) and loperamide. Azithromycin compared favorably with fluoroquinolones in trials that did not include the use of loperamide, but combination therapy has not, to our knowledge, been studied to date. Methods. A randomized, double-blind trial was conducted at Incirlik Air Base, Turkey, from June 2003 through August 2004. Adults from the United States with noninflammatory diarrhea were randomized to receive a single dose of azithromycin (1000 mg; 106 persons) or levofloxacin (500 mg; 101 persons) plus loperamide (4 mg initially and as needed thereafter). Volunteers maintained a symptom diary and were evaluated on days 1, 3, and 7 after treatment. Results. No differences were noted with respect to pretreatment symptoms or pathogen distribution. Enterotoxigenic Escherichia coli was the most common pathogen isolated (from 45% of patients in the azithromycin group and 42% of patients in the levofloxacin group), and Campylobacter species was the second most common pathogen isolated (from 6% of patients in the azithromycin group and 9% of patients in the levofloxacin group). Median time to last diarrheal stool (azithromycin group, 13 h; levofloxacin group, 3 h), median time to resolution of associated symptoms (2 days), and additional loperamide usage (azithromycin group, 39% of patients; levofloxacin group, 34% of patients) were similar between groups. Azithromycin use was associated with more nausea in the 30 min after dosing (azithromycin group, 8% of patients; levofloxacin group, 1% of patients; P = .004), but no vomiting or other adverse events were noted in either group. Conclusions. Single-dose treatment with azithromycin (1000 mg) and loperamide is as effective as single-dose treatment with levofloxacin (500 mg) and loperamide for noninflammatory diarrhea. Although nausea after dosing is uncommon, it is more frequently associated with azithromycin than with levofloxacin. Future studies should focus on determining whether lower doses of azithromycin would decrease the frequency of nausea and decrease treatment costs without affecting efficacy.