This study will examine the safety and effectiveness of an experimental drug called J695 for treating patients with Crohn's disease-a long-term recurring inflammation of the small and large intestine. This disease is currently treated with steroids, sulfasalazine (Azulfidine), 5-ASA drugs (Pentasa, Asacol), immune suppressants, antibiotics, and an antibody against TNF-alpha. Despite the number and variety of available therapies for Crohn's disease, many patients do not respond adequately to treatment or they develop severe side effects from the medicines. Therefore, new treatments must be developed. J695 is an antibody that is identical to a human antibody but chemically changed so that it can attach to and eliminate an inflammatory chemical made by the body called interleukin-12 (IL-12). Animal studies have shown that eliminating IL-12 with an antibody can prevent inflammation in the gut and can also heal inflammation that has already developed.