The courses of 90 patients with left-sided ulcerative colitis that was unresponsive or intolerant to conventional therapy were retrospectively reviewed. They had been treated with 5-aminosalicylic acid enemas (mesalamine) on a long-term basis. After an initial 12-week course of treatment, 87% of the patients had improved by at least one grade of inflammation (improvement), and 54% of these were asymptomatic with normal colonic mucosa (remission). Overall, there was an 80% remission rate by 34 weeks. Remission rate was not affected by extent of sigmoid or left-sided colon disease before treatment or prior medication use for ulcerative colitis. Treatment with mesalamine enemas allowed patients to decrease or discontinue glucocorticoid treatment. Patients treated for relapse episodes responded as well as they did to the first course of treatment, whether the relapse occurred after discontinuation of mesalamine or during a tapering of the dose. In conclusion, extending mesalamine treatment to at least 34 weeks was beneficial in inducing a complete remission in 80% of patients unresponsive to conventional therapy.