Abstract: AIM: A new method to measure median effective dosage based on the principle of sequential trial was designed: improved robbins-monro process. To explore the reliability, advantage and disadvantage of the method. METHODS: Median lethal doses(LD₅₀) of procaine and pentetrazole were detected and compared with improved robbins-monro process and Classical Bliss method. RESULTS: LD₅₀ of procaine and pentetrazole with the improved robbins-monro process were 207.5 mg/kg and 107.2 mg/kg respectively, LD₅₀ with the Bliss method were 206.1 mg/kg and 101.2 mg/kg respectively. Results indicated that the LD₅₀ with improved robbins-monro process is similar with Bliss method, while the new method is fewer animals and time consuming and simpler to calculate. CONCLUSION: Improved robbins-monro process is suitable to mesure median effective dose, for example LD₅₀ or ED₅₀, for the drug which efficicy is rapid and point is easy to determine the end.

Key words: Improved robbins-monro process, Bliss method, Median lethal dose (LD₅₀), Procaine, Pentetrazole