This paper summarizes the basis of prescription for automated peritoneal dialysis (APD) established during a French national conference on APD. Clinical results and literature data show that peritoneal clearances are closely determined by peritoneal permeability and hourly dialysate flow rate, independently of dwell time or number of cycles. With APD, peritoneal creatinine clearance increases according to the hourly dialysate flow rate to a maximum (plateau), then decreases because of the multiplication of the drain-fill times. The hourly dialysate flow giving the maximum peritoneal creatinine clearance is defined as the "maximal effective dialysate flow" (MEDF). MEDF is higher for high peritoneal permeabilities: MEDF is 1.8 and 4.2 L/hr with nocturnal tidal peritoneal dialysis (TPD) for a 4-hr creatinine dialysate-to-plasma ratio (D/P) of 0.50 and 0.80, respectively. With nightly intermittent peritoneal dialysis (NIPD), MEDF is 1.6 and 2.3 L/hr for a D/P of 0.50 and 0.78, respectively. Under these conditions, tidal modalities can only be considered as a way to increase the MEDF. Using the MEDF concept for an identical APD session duration, the maximal weekly normalized peritoneal creatinine clearance can vary by 340% when 4-hr D/P varies from 0.41 to 0.78. APD is not recommended when 4-hr creatinine D/P is lower than 0.50. However, the limits of this technique may be reached at higher peritoneal permeabilities in anurics because of the duration of sessions and/or the additional exchanges required by these patients.