A study was undertaken to evaluate the short-term reproducibility of peritoneal equilibration test (PET) results. Nine patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis underwent PETs under similar conditions on 2 consecutive days. Dialysate samples were obtained at 0 hours, midcycle, and at the end of exchange. There were no significant differences between the mean ratios at 4 hours for creatine, urea nitrogen, potassium and protein, and glucose between PET 1 and PET 2. A standard PET is highly reproducible when repeated under similar conditions. Reproducibility is better for ratios of creatinine, glucose, urea nitrogen, and potassium than for protein.