The pharmacokinetics of gentamicin were examined in two functionally anephric patients undergoing peritoneal dialysis (PD). Peritoneal dialysis effectively decreased the gentamicin half-life (t1/2 beta) by 73 and 78% while increasing total body clearance [QB(ml/min/kg] of gentamicin 4.3- and 3.4-fold. The appreciable variability in gentamicin pharmacokinetics among renal failure patients being peritoneally dialyzed may necessitate dosage adjustments based on rapid and accurate measurement of serum gentamicin concentrations.