Pulmonary function has been assessed in 36 outpatients with inflammatory bowel disease. The CO2 transfer factor was significantly reduced in patients as compared with matched controls (P < 0.01). The reason for this reduction is not clear, but it is unlikely to be due to sulfasalazine (salazosulphapyridine). [Sulfasalazine, which is regularly used in the treatment of inflammatory bowel disease (IBD), particularly ulcerative colitis, has occasionally been implicated as a cause of fibrosing alveolitis.].