BACKGROUND The major determinants of pulse wave velocity (PWV) in haemodialysis (HD) patients are not fully known. We studied chronic HD patients to assess the effect of cyclic variations in both hydration status and blood pressure on PWV. METHODS Twenty patients were examined along three consecutive HD sessions and interdialysis periods during a week-long period. Twenty healthy subjects and 20 chronic kidney disease (CKD) patients (stage 5) were evaluated as controls. RESULTS In contrast to controls, HD patients showed cyclic changes in PWV. Specifically, PWV values in HD patients were significantly higher prior to the first HD session of the week compared with values measured prior to the other two HD sessions during the week. In addition, PWV showed significant reductions during each dialysis session (15.6 +/- 5.2 to 9.3 +/- 2.3, 13.4 +/- 4.0 to 8.7 +/- 2.4, and 12.4 +/- 2.6 to 9.2 +/- 2.2 m/sec, before and after the first, second and third weekly dialysis sessions, respectively). Nevertheless, the weighted weekly values of PWV in HD patients (10.8 +/- 5.7 m/sec) were similar to those in CKD patients (9.9 +/- 4.2 m/sec). The HD ultrafiltration rate (UF) was significantly correlated with intradialysis PWV changes (r = 0.465; P < 0.001) and with after dialysis PWV values (r = -0.654; P < 0.0001). Blood pressure changes during dialysis were weakly correlated with post-dialysis PWV (r = -0.267; P < 0.05), but not with PWV changes during dialysis. CONCLUSIONS In chronic HD patients, single PWV values varied widely during 1 week of HD sessions, whereas the weighted level showed only a slight increase. The major determinant of changes in PWV during HD appears to be the alterations in hydration status; the most representative time point for PWV measurements during HD corresponds to the interdialysis days.