Improving clearances on peritoneal dialysis involves either more exchanges, greater fill volume, or both. An increase in the number of exchanges is inconvenient, resulting in noncompliance. Therefore, the best option is to increase the exchange volumes; however, patients are often reluctant for fear of discomfort. We tested the tolerance of 20 patients blinded to randomly sequenced volumes of 2, 2.5, and 3 L, performed incenter by the dialysis nurse. Each patient underwent one to three exchanges with each volume. At the end of a 4-hour dwell, the patient scored discomfort and estimated the infused volume. Only one study exchange was performed each day; the rest of the time, the patient continued his or her usual prescription. Fifteen of the patients (75%) were not able to identify the exchange volumes. Four of the five patients who determined the correct exchange volume for 67% to 78% of the exchanges (P < 0.04 compared with 33% expected by chance) had a body surface area greater than 1.75 m2. Of 123 exchanges, 84% were associated with no discomfort, 10% with mild discomfort, and 6% with moderate discomfort. Patients were not more likely to have discomfort with 3-L compared with lower fill volumes. Peritoneal clearances of creatinine (6.1 v 6.6 v 7.7 mL/min/1.73 m2) and urea nitrogen (7.3 v 8.6 v 9.5 mL/min) were progressively greater with increasing exchange volumes (P < 0.001). We conclude that the majority of small as well as large patients will tolerate 2.5- and 3-L exchange volumes. If encouraged to do so, many patients could tolerate greater exchange volumes than they are presently using. Exchange volumes should be readily increased as residual renal function declines.