Blood pressure (BP) of patients on continuous ambulatory peritoneal dialysis (CAPD) must be well controlled. The present study tests a clinical impression that BP recordings are higher with dialyzate within the peritoneal cavity than after it is drained out. 8 CAPD patients had systolic BP, diastolic BP and heart rate measured both with dialyzate in situ and after drainage. Paired t-tests showed systolic BP and diastolic BP but not heart rate to be significantly (P less than 0.05) higher with dialyzate in situ. To avoid a false impression of good BP control it is recommended patients on CAPD measure BP with dialyzate in situ.