BACKGROUND Motility disorders are believed to be of major pathogenetic importance in small-intestinal bacterial overgrowth (SIBO). The aim of this study was to investigate interdigestive and postprandial motility in a group of patients with SIBO and to compare the results with those of healthy volunteers. METHODS Twenty healthy subjects and 14 patients with SIBO were included. Exclusion criteria were obvious predisposing conditions. Antroduodenojejunal pressure recording was performed after an overnight fast. After a 5-h interdigestive recording a standard meal was given, and postprandial recording performed for 30 min. RESULTS Significantly fewer patients than healthy subjects had phase-III activity in the antrum (3 of 14 versus 15 of 20; P < 0.01), and more patients lacked phase III completely (5 of 14 versus 0 of 20; P < 0.05). Propagated single contractions in the proximal duodenum during late phase II and postprandially were also significantly reduced (1 (0-5) versus 8 (5-12) per 30 min (median; interquartile range (IQR)) (P < 0.01) and 0.5 (IQR, 0-6.5) versus 8 (IQR, 6-13) per 30 min (P < 0.01), respectively). In the distal part of the duodenum the patients had significantly prolonged duration of phase III (7.8; IQR, 5.6-9.2 versus 5.9; IQR, 4.2-6.6 min) (P < 0.05) and increased motility index of phase III (6685; IQR, 4870-9999 versus 3605; IQR, 2579-5544 mm Hg x min/30 min) (P < 0.05), late phase II (10,285; IQR, 6105-11,384 versus 6650; IQR, 4639-9102) (P < 0.05), and postprandially (12,960; IQR, 8454-18,644 versus 7917; IQR, 6132-10,551) (P < 0.05). Retrograde contractions predominated in the late part of phase III in the proximal duodenum in both groups. The cycle length of the MMC and the number of clustered contractions showed no difference between the two groups. CONCLUSIONS A significant proportion of patients with SIBO, compared with healthy subjects, lack interdigestive phase-III activity, not only in the small intestine but also in the gastric antrum. They also have fewer propagated contractions in the proximal duodenum during interdigestive phase II. On the other hand, the motility index in the distal part of the duodenum was higher in patients with SIBO during phase III, late phase II, and postprandially. The results are compatible with a reduced clearing function in the stomach and proximal duodenum and/or a compensatory increase of motility in the region of the duodenojejunal flexure.