In order to confirm the theory of administration at the optimal time in The Yellow Emperor’s Internal Classic

effects of administration of Herba Epimedii at the optimal time on the level of sexual hormones in young mice were investigated to explore the relationship between the time of administration and the effect. Results indicated that （1） Yin Yang Huo Decoction had sexual hormone-like actions

increasing weight of uterus and serum estradiol （E2） content in the female mice

increasing serum testosterone （T） content in the male mice; （2） The administration at Mao （the period of the day from 5 a. m. to 7 a. m.） and You （from 5 p. m. to 7 p. m.）. hours influenced the increases of uterus weight and serum E2 content in the female mice and serum T content in the male mice to a certain degree

the action at Mao being stronger than that at the You. It is suggested that administration for tonifying the kidney and strengthening Yang in the early morning has the best effect.