Background/Aim: Increases in microalbuminuria and endothelin (ET-1) are involved in the development of ulcerative colitis (UC) and in its progress. Because granulocyte and monocyte adsorption apheresis has proven to be useful in the treatment of UC, we examined whether urinary albumin excretion and plasma ET-1 concentrations are altered and whether granulocyte and monocyte adsorption apheresis affects the concentrations of these two factors in patients with active UC. Methods: Twenty patients with active UC and 20 age-matched healthy volunteers (our hospital staffs) were included in this study. UC patients were randomly divided into two treatment groups: a granulocyte and monocyte adsorption treatment group (n = 10) and a conventional treatment group (n = 10). The urine albumin/creatinine ratio, plasma ET-1 concentration and tumor necrosis factor (TNF)-α were determined before and after treatment and compared between 2 treatment groups. The 10 adsorption treatment patients underwent 5 consecutive weekly apheresis sessions, each of 60 min duration at a flow rate of 30 ml/min. Results: The urine albumin/creatinine ratio in UC patients (6.4 ± 2.2 mg/mmol) were higher than that in healthy subjects (1.0 ± 0.7 mg/mmol, p < 0.01). In addition, the plasma ET-1 level in UC patients (3.5 ±1.5 pg/ml) was higher than that in healthy subjects (0.8 ± 0.4 pg/ml, p < 0.01). Plasma TNF-α was detected in UC patients (18.8 ± 8.4 pg/ml), but not in healthy subjects. The urine albumin/creatinine ratio was highly correlated with the plasma ET-1 level (r = 0.62; p < 0.01) and plasma TNF-a level (r = 0.66, p < 0.01). Granulocyte and monocyte adsorption apheresis reduced the urine albumin/ creatinine ratio from 6.6 ± 2.4 to 1.8 ± 0.6 mg/mmol (p < 0.01), reduced the plasma ET-1 level from 3.7 ± 1.6 to 1.4 ± 0.6 pg/ml (p < 0.05) and reduced the plasma TNF-α from 19.2 ± 8.6 to 3.8 ± 1.2 pg/ml (p < 0.01). Conventional treatment did not affect these factors. Conclusion: Our data suggest that increases in the urine albumin/creatinine ratio, ET-1 and TNF-α play an important role in active UC and that granulocyte and monocyte adsorption apheresis is effective in ameliorating such increases.