Background/Aims: In the patients with ulcerative colitis (UC), folate levels are frequently diminished due to poor oral intake, inadequate absorption, and increased metabolic demand of colonic mucosa. The aim of this study was to measure the folate concentrations in serum, red blood cell (RBC) and colonic mucosa of the patients with UC and normal control, and then to evaluate the relationship between the folate concentrations and clinical variables. Methods: Fifteen patients with UC and fifteen normal controls were enrolled. The folate concentrations in serum, RBC and colonic mucosa were measured by radioimmunoassay. Colonic mucosa was obtained by colonoscopic biopsy and its folate concentration was assessed according to the clinical variables. Results: The folate concentrations in serum and RBC were lower in the patients with UC than in control (serum: 3.56±1.58 ng/mL vs. 3.84±1.57 ng/mL, RBC: 311.4±105.3 ng/mL vs. 333.4±102.7 ng/mL) without statistical significance (p=0.94, p=0.19, respectively). However, the folate concentration in colonic mucosa was significantly lower in the patients with UC (288.64±65.84 ng/g tissue) than in control (480.6±163 ng/g tissue, p<0.001). There was a significant inverse correlation between the duration of UC and folate concentration in colonic mucosa (p<0.05). Conclusions: The measurement of folate concentration in colonic mucosa may be a direct method to evaluate of regional folate status in patients with UC, compared to those of serum and RBC. The long duration of UC induces low folate concentration in colonic mucosa. (Kor J Gastroenterol 1999;34:190 - 196)