OBJECTIVE: Free water transport (FWT) can be calculated after a dwell of 1 hour with a 3.86% glucose solution using sodium kinetics (mini-PET, as developed by LaMilia et al.). This requires measurement of the intraperitoneal volume after drainage of the abdomen. Since valuable information of a 4-hour peritoneal equilibration test (PET) may be lost, the aim of the present study was to investigate whether temporary drainage of the peritoneal cavity after 1 hour and re-instillation thereafter would influence the results of the 4-hour PET. Methods and PATIENTS: Two PETs were performed in 10 stable peritoneal dialysis (PD) patients (mean age 59 +/- 13 years, mean duration on PD 33 +/- 15 months) within a mean period of 54 (range 13 - 104) days: one standardized 4-hour PET using 3.86% glucose (PET A) and one with drainage after 1 hour followed by re-instillation (PET B). RESULTS: Mean total ultrafiltration (UF) of PETs A and B was 667 +/- 210 mL and 621 +/- 206 mL (NS). Mean FWT at 60 minutes was 164 +/- 74 mL and mean UF through the small pores was 204 +/- 181 mL; FWT correlated well with total UF (r = 0.720, p = 0.019). Classification of transport categories was identical for 9 of the 10 patients. Comparison of 1-hour and 4-hour results in test B showed a good correlation between dialysate-to-plasma ratios (D/P) of creatinine and urea and D(t)/D(0) ratios of glucose. CONCLUSION: A 4-hour 3.86% glucose PET, including temporary drainage after 1 hour for assessment of free water transport, does not influence the results of D/P creatinine or D(t)/D(0) glucose and gives essential additional information on aquaporin function.