The urinary excretion rates of nitrate (NO3) and nitrite (NO2) were monitored in 14 patients with active ulcerative colitis during treatment using hydrocorti-sone and sulfasalazine. During the active phase of the disease, the NO3 excretion was significantly higher in the patients than in healthy controls (n – 6, p < 0.05), although it varied considerably among the patients. During the healing phase, the NO3 excretion decreased concurrently with improvement of symptoms and colorectal ulceration, but the NO2 excretion increased. During the inactive phase of the disease, the NO3 and NO2 excretions were significantly lower than during the active phase, and the NO2/NO3 ratio resembled that in the healthy controls. In contrast, a patient who failed to respond to treatment showed continuously high NO3 and NO2 excretion rates. These results indicate that urinary NO3 and NO2 excretions vary with the disease state in ulcerative coliti