In order to better justify the use of antibiotics in the treatment of Crohn's disease, the Antibiotics for Colonic Crohn's Disease trial has been designed to determine if ciprofloxacin and metronidazole combination therapy is effective in the treatment of active Crohn's disease of the colon. This two arm, multi-centre, randomized, double-blind, parallel-group, placebo-controlled study will involve 136 patients with mild to moderate active Crohn's disease of the colon (with or without ileal involvement), as defined by a Crohn's Disease Activity Index (CDAI) score between 220 and 450.