Background : The aim of this study was to characterize the nature and elucidate the pathogenesis of hemodialysis ascites(HA), especially with regard to the levels of Serum Ascites Albumin radient(SAAG) and the degrees of hemodialysis adequacy(Kt/Vurea). Methods : In the study group, seven cases of HA which had developed in 6 patients from Feb. 1997 through July 1998 were included. In the control group, 24 cases which had not developed HA were included. The study design was a retrospective. Analysis of ascites on WBC, total protein and albumin, cytology, ADA(Adenosine deaminase), osmolality, SAAG and routine work-up were performed in HA group. Serum total protein and albumin, C-reactive protein(CRP), osmolality, and routine liver function test were also checked. Kt/Vurea and weekly Kt/Vurea were calculated in both group. In statistical analyses, t-test and chi-square test were used.Results : Mean SAAG of HA was >1.1(1.49±0.40) gm/dL, and mean concentration of total protein of HA was >2.5(4.26±0.58) gm/dL. The mean of weekly Kt/Vurea of patients with HA(2.61±0.85) was significantly lower than that of patients without HA(3.48±0.90)(p<0.05). Positive ratio of CRP in patients with HA was higher than that of patients without HA(p<0.05). Mean concentration of serum total protein was significantly higher in patients with HA than that of patients without HA but with comparable weekly Kt/Vurea levels(p<0.05).Conclusion : It is regarded that the nature of HA is an exudate having high SAAG over 1.1 gm/dL. Low weekly Kt/Vurea is suggested as a cause of HA. Chronic inflammation was also regarded as an important factor causing HA.(Korean J Med 59:283-289, 2000)