The human migrating motor complex (MMC) and sleep cycle have a similar periodicity, and there is some contention as to whether these biorhythms are linked. In irritable bowel syndrome (IBS), episodes of intestinal dysmotility have been described almost exclusively during wakefulness, but IRS patients often complain of poor sleep, and it has been suggested that IBS patients have increased rapid eye movement (REM) sleep. This study sought to identify any associations between sleep stage and small intestinal motility and any objective sleep abnormalities in IBS. Nocturnal motility was recorded from six small intestinal sensors mounted on a fine nasoenteric catheter in eight IBS patients and 10 healthy volunteers. Polysomnography to determine sleep stage was recorded simultaneously. The proportions of time awake, in non-REM and REM sleep was similar in controls and IBS. REM latency did not differ between the two groups despite increased depression in the IBS patients (Hamilton Depression Rating of 8.3 +/- 1.7 in IBS, 3.0 +/- 0.7 in controls, P < 0.01). Nocturnal motility was similar, with phase I occupying most of the MMC cycles. There was no temporal association between MMCs and sleep stage, with no synchrony of phase III for REM episodes. The mean motility index of 4.5 +/- 0.4 during wakefulness was greater than during all sleep stages (P < 0.05). During non-REM sleep stages 1 and 2, motility index of 3.2 +/- 0.3 was greater than 2.3 +/- 0.2 during stages 3 and 4 (P < 0.05), but similar to motility index of 3.3 +/- 0.4 during REM sleep. This sleep architecture and nocturnal small intestinal motility are normal in IBS.(ABSTRACT TRUNCATED AT 250 WORDS)