Lung toxicity associated with 5-aminosalicylate (5-ASA) agents is a rare entity. We report the case of a 32-yr-old woman with ulcerative colitis who developed progressive shortness of breath while taking one of the 5-ASA drugs, oral mesalamine. Bilateral pulmonary infiltrates, peripheral eosinophilia, and histological findings consistent with acute pneumonitis characterized the lung injury. Although the differential diagnosis is broad, mesalamine-induced lung damage must be considered in patients who develop unexplained respiratory symptoms while taking this agent.