To assess the value of measurements of superior mesenteric artery flow using Doppler ultrasound for detecting disease activity in patients with proven or suspected Crohn's disease.Superior mesenteric artery flow was measured prospectively in 31 patients with known or suspected small-bowel disease. Sixteen patients were known to suffer from Crohn's disease and were suspected of having active disease. Fifteen patients had abdominal complaints without a specific diagnosis. Enteroclysis was used as the standard of reference to detect Crohn's disease, to define the location of small-bowel Crohn's disease, and to assess disease activity by demonstrating cobblestoning. Disease activity was further substantiated by clinical signs, laboratory values, and clinical follow-up.Ten patients with active disease on enteroclysis made up group 1. Group 2 comprised nine patients known to have Crohn's disease but without active disease (inactive small-bowel disease). The remaining 12 patients made up group 3. In group 1, the flow volume values were significantly higher than those in group 2 and group 3: 738 +/- 411 (mean +/- SD) versus 364 +/- 101 and 300 +/- 91, respectively (p0.05).Whereas the initial diagnosis of small-bowel involvement in Crohn's disease may rely on enteroclysis, Doppler measurements of superior mesenteric artery flow are useful to monitor the activity of Crohn's disease.