The mechanisms of transperitoneal sodium transport during hypertonic peritoneal dialysis were evaluated by kinetic modelling. A total of six nested mathematical models were designed to elucidate the presence or absence of diffusive, non-lymphatic convective and lymphatic convective solute transport. Experimental results were obtained from 26 non-diabetic patients undergoing peritoneal dialysis. The model validation procedure demonstrated that only diffusive and non-lymphatic convective transport mechanisms were identifiable in the transperitoneal transport of sodium. Non-lymphatic convective sodium transport was the most important quantitative transport mechanism during the first 90 min of the dwell. Significant sodium sieving was demonstrated and explains the observation of hypernatremia in dialysis with hypertonic dialysis fluid.