OBJECTIVE:To establish a scientific evidence for evaluation of individualized administration among children.METHODS:Hydrocortisone probe was used for determination of CYP3A activity in children with quantitative method.RESULTS:CYP3A activity in the health children volunteers showed Gaussian distribution in the form of natural logarithm,the average value was1.69?1.04,with the value of1.63?0.99in males and1.75?1.09in females.CONCLUSION:There is no significant difference in CYP3A activity between the two sexes.