A two-compartment model of patient-artificial kidney system consisting of a cerebrospinalfluid(CSF)and a body liquor compartments have been presented.With the model,the mechanism ofdisequilibrium syndrome occurred in a patient undergoing hemodialysis has been discussed to simulatethe CSF pressure transients.Urea,as an uretic toxin,was injected into dogs and in vivohemodialysis experiments have been performed under clinical conditions.The parameters in the sol-ution,G and K,have been determinde from experiments and are in good agreement with those re-ported under normal physiological conditions and in previous investigations.