Purpose: Recently, the plasma refilling coefficient (mean Kr) was proposed as a new marker of vascular permeability during hemodialysis (HD). However, there are only a few reports about its utility in clinical examination. Therefore, in this study, we examined the usefulness of mean Kr as a marker of dry weight (DW) in chronic HD patients. Methods: In 41 stable maintenance HD patients, Ht, TP and body weight change were measured before and after HD for 12 months, Mean Kr was calculated from these parameters 446 times. Then, we divided all mean Kr data into four groups according to the absolute value as follows: group I, 0<mean Kr≤1 (n=148); II, 1<mean Kr≤4 (n=218); III, 4<mean Kr (n=45); IV, mean Kr<0 (n=35). Results: 1) There was no correlation between mean Kr and the speed of ultrafiltration during HD, and TP before HD. 2) CTR was 51.3±0.4 in group I, 52.8±0.4 in II, 55.9±0.8 in III and 57.9±1.2% in IV. CTR was significantly smaller in group I than in group III and IV, and in group II than in group IV. 3) The reduction rate of mean arterial pressure (MAP) during HD was larger in group I compared to the other groups. 4) The necessity of saline infusion at HD-related hypotension was higher in group I compared to the other groups. 5) The changes of circulating blood volume during HD (%ΔBV) was -4.2±0.1 in group I, -2.4±0.1 in II, -0.6±0.1 in III and 1.0±0.1% in IV. The difference of %ΔBV was significant in each of the four groups. 6) There was significant positive linear correlation between the ratio of mean Kr (mean Kr/mean Kr) and atrial natriuretic peptide (ANP/ANP) over 5 consecutive months (y=0.73±0.29X, r=0.47, p<0.01, n=36). Conclusions: Mean Kr may be useful to determine the DW in chronic HD patients because it reflected other markers for DW determination. There was the possibility that an adequate value for mean Kr ranged from 1 to 4ml/min/mmHg during HD.