Opponent's comment.

Effect of frequent or extended hemodialysis on cardiovascular parameters: a meta-analysis. A systematic review of the effect of nocturnal hemodialysis on blood pressure, left ventricular hypertrophy, anemia, mineral metabolism and health-related quality of life. et al. Frequent hemodialysis schedules are associated with reduced levels of dialysis-induced cardiac injury (myocar-dial stunning). Dialysis outcomes and analysis of practice patterns suggests the dialysis schedule affects day-of-week mortality. Economic evaluation of frequent home nocturnal hemodialysis based on a randomized controlled trial. Effects of 6-times-weekly versus 3-times-weekly hemodialysis on depressive symptoms and self-reported mental health: Frequent Hemodialysis Network (FHN) Trials. et al. Survival and hospitalization among patients using nocturnal and short daily compared to conventional hemo-dialysis: a USRDS study. Labriola et al. [1] support that available randomized studies show no clear survival benefit of short daily haemodialysis (SDHD) or frequent nocturnal haemodialysis (NHD). In the Frequent Hemodialysis Network (FHN) trial [2], mortality was not a prespecified separate primary end point; thus, it was clear from the start that the study was underpowered to detect a difference in mortality alone. In this case, the proper comment seems to be that 'absence of evidence does not mean evidence of absence of effect'. The FHN trial demonstrated among other a significantly greater regression in the left ven-tricular mass in favour of SDHD; at least this effect cannot be neglected, as it clearly affects survival in haemodialysis patients [3]. With regard to observational studies, improved survival of 15–45% with enhanced-frequency dialysis (i.e. home NHD) was previously noted in several studies [4, 5]. We agree with Labriola et al. [1] that this outcome could be influenced by selection bias, higher dialysis dose, setting and other factors.