Dialysis adequacy indices that may be used to evaluate the efficiency of small-solute removal include Kt/V, fractional solute removal (FSR), and equivalent urea clearance (EKR). To analyze possible relationships between those indices, we used the two-compartment variable-volume urea kinetic model to simulate several dialysis modalities: hemodialysis (HD) performed three times or six times weekly, automatic nightly peritoneal dialysis (PD), and continuous ambulatory PD. Instead of targeting a chosen Kt/V value, we selected a weekly FSR of 1.81 as the target adequacy index. We determined hemodialyzer clearances and diffusive mass transport parameters for the peritoneal membrane that yielded the desired value of FSR for a typical patient and dialysis schedule. By theoretic analysis, EKR and FSR are proportional: EKR/FSR = V/Tc, where V = urea distribution volume in the body and Tc = time of the dialysis cycle, usually 1 week. Thus, FSR and EKR have the same meaning and scaling in PD and HD, and may be equivalently applied for assessment of dialysis efficacy.