Alterations in both gastric emptying (GE) and small bowel motility have been reported in irritable bowel syndrome (IBS); the relationship, however, between these different measures of upper gut motor function in IBS has not been assessed. The aims of this study were therefore: (1) to compare the prevalence and characteristics of altered small bowel motility in IBS patients with and without delayed GE; and (2) to assess the interrelationships between fasting and postprandial small bowel motility in IBS, accounting for delayed GE. Forty-four IBS patients and 25 healthy controls underwent 24 hr ambulant recording of interdigestive and digestive small bowel motility. On a separate occasion the IBS patients had GE of both solids and liquids measured by a dual-isotope scintigraphic technique. Thirty-nine percent of IBS patients had delayed GE. Patients with normal GE had no interdigestive small bowel abnormalities. However, in patients with delayed GE fasting phase II burst frequency was higher than in controls [median 0.21/hr (IQR 0.15-0.34) vs 0.06/hr (0-0,16), P = 0.004]. Postprandially, abnormal phase III-like activity was higher in diarrhea-predominant IBS patients (0-0.08/hr vs 0/hr, P = 0.01), than in patients with normal GE or controls. Furthermore, IBS patients with delayed GE did not have the normal correlation between fasting and postprandial motor parameters (percentage occurrence of clustered contractions, postprandial pattern duration vs preceding MMC cycle length). In conclusion, small bowel motor dysfunction occurs more frequently in IBS patients with concomitant gastroparesis than in patients with normal GE. These findings provide further evidence that a neuropathic process may contribute to the pathogenesis of IBS in a subgroup of IBS patients.