Free radicals have been suspected to play an important role in the pathogenicity of chronic pancreatitis. We reviewed studies on free radicals in chronic pancreatitis in both c1inical and experimental aspects. Many clinical studies have provided circumstantial evidence for the close relation between free radicals and chronic pancreatitis. However, few experimental studies in animals on relation between free radicals and chronic pancreatitis have been reported, because adequate experimental models for elucidating a pathological role of free radicals in chronic pancreatitis have not been established. The research concerning the role of free radicals in chronic pancreatitis is expected to improve our understanding the pathological mechanisms of the disease.