To compare the clinical and antimicrobial efficacy of besifloxacin ophthalmic suspension 0.6% with that of moxifloxacin ophthalmic solution 0.5% for the treatment of bacterial conjunctivitis. Multicenter, randomized, double-masked, parallel-group, active-controlled, noninferiority study. Patients 1 year of age or older with clinical manifestations of bacterial conjunctivitis. Eligible patients were randomized to either besifloxacin suspension or moxifloxacin solution, instilled in the infected eye(s) 3 times daily for 5 days, and participated in study visits on days 1, 5 (+/-1 day), and 8 (+1 day). Assessments included clinical evaluation of signs and symptoms, visual acuity, biomicroscopy, and culture of the infected eye(s) at each visit, as well as direct ophthalmoscopy on days 1 and 8. The primary efficacy end points were clinical resolution and microbial eradication of baseline bacterial infection on day 5 in patients with culture-confirmed bacterial conjunctivitis. Secondary end points included clinical resolution and microbial eradication on day 8, individual clinical outcomes, microbial and clinical outcomes by bacterial species, and safety. A total of 1161 patients (533 with culture-confirmed bacterial conjunctivitis) were randomized. Based on the 95% confidence interval (CI) of the difference, besifloxacin was noninferior to moxifloxacin for clinical resolution on day 5 (58.3% vs. 59.4%, respectively; 95% CI, -9.48 to 7.29) and day 8 (84.5% vs. 84.0%, respectively, 95% CI, -5.6% to 6.75%) and for microbial eradication on day 5 (93.3% vs. 91.1%, respectively, 95% CI, -2.44 to 6.74) and day 8 (87.3% vs. 84.7%; 95% CI, -3.32 to 8.53). There was no statistically significant difference between the 2 treatment groups for either efficacy end points on days 5 or 8 (P>0.05). Besifloxacin and moxifloxacin were well tolerated. The cumulative frequency of ocular adverse events was similar between treatments (12% and 14% with besifloxacin and moxifloxacin, respectively). However, eye irritation occurred more often in moxifloxacin-treated eyes (0.3% for besifloxacin vs. 1.4% for moxifloxacin; P = 0.0201). Besifloxacin ophthalmic suspension was non inferior to moxifloxacin ophthalmic suspension and provided similar safety and efficacy (clinical and microbiological) outcomes when used for the treatment of bacterial conjunctivitis. Proprietary or commercial disclosure may be found after the references.