In Crohn's disease, antibiotics are used with variable efficacy, suggesting that some patients are more likely to respond. The aim of this study was to determine whether Crohn's patients with predominant serum antibody reactivity toward bacterial antigens OmpC and/or I2 were more likely to achieve remission with antibiotics. Patients with ileal or ileal with right-sided colonic Crohn's disease were studied in a double-blind trial of budesonide alone or budesonide plus metronidazole and ciprofloxacin. In the budesonide plus metronidazole and ciprofloxacin group, patients with OmpC/I2 predominant profiles had the highest remission rate, whereas the group with no antibody predominant profiles had the lowest rate. In the budesonide group, patients with the OmpC/I2 predominant profile had the lowest remission rate, and the no-antibody group rate was higher. Although not statistically significant, these results support further testing to determine whether predominant serum reactivity to certain bacterial antigens may be a marker for efficacious use of antibiotics.