Abstract:Circadian rhythms have been observed obviously for both normal and pathological mice when Radix et Rhizoma Rhei is given. As a rule, the catharsis becomes stronger when Radix et Rhizoma Rhei is given at night than during the day. The rhythms vary with different pathological models. Compared with the normal mice, the circadian rhythms tend to be clearer for those mice excited by thyroidization. However, thyroidization makes the mice less sensitive to the dosage change of Radix et Rhizoma Rhei, while the mice weakened by tabazole administration show the reverse reaction.