The complement inhibitor K-76 (Otsuka Pharmaceutical Co., Osaka, Japan) was clinically evaluated as a new drug for treatment of active stage ulcerative colitis (UC). As monotherapy, K-76 proved effective in four of five cases. Furthermore, in patients with active stage UC that continued despite administration of corticosteroid hormone and salicylazosulphapyridine (so-called refractory UC), concomitant administration of K-76 was effective in seven of 21 cases. Thus, we believe that the multifunctional agent K-76 will provide clinicians with a new therapeutic approach to inflammatory bowel diseases, including UC and Crohn's disease.