The response of a kidney patient to treatment using a microencapsulated urease artificial kidney (MUAK) system was modelled. The model was used to simulate the patient's response and reactor performance for an initial blood urea concentration of 10 mM and a MUAK void volume of 0.5. The performance of the reactor was strongly dependent on the enzyme activity. An optimal activity of 10 mM sec-1 was achieved in the analysis. After operation for 4 h at a flow rate of 200 ml min-1, the reduction in blood urea concentration for reactor dimensions of 2 x 10 cm, 2 x 20 cm, 4 x 10 cm and 4 x 20 cm were 38%, 52%, 60% and 62%, respectively. The effect of flow rate on the performance of urea removal was studied using the reactor dimensions of 4 x 10 cm (optimal design). The results for flow rates of 100, 200, 300 and 400 ml min-1 predicted blood urea reductions of 38, 60, 70 and 76%, respectively. Although, the conversion of urea in the reactor decreased from 100% to 96% for the respective flows of 100 to 400 ml min-1, the high turnover of reactor volume at a higher flow rate was responsible for the improved reduction of the patient's blood urea level. The model has the ability to predict the performance of the MUAK and the patient's blood urea level simultaneously, at various operating conditions.