This paper describes a new technique for ambulatory long-term monitoring of small-bowel motility. Intraluminal pressure was measured with a silicon catheter with two strain-gauge transducers spaced 15 cm apart. Pressure data were stored in a portable memory unit. Initial studies showed that a recording frequency of 2 Hz was sufficient for obtaining reliable motility measurements. Twelve-hour recordings of motility in the upper jejunum were done in 12 healthy volunteers. After a 1964-kJ meal the median duration of fed-state motility was 4.6 h (3.4-5.3 h, interquartile range). The activity front of the migrating motor complex propagated with a velocity of 2.7-5.3 cm/min, and the median cycle length was 77 (40-103) min. The frequency of contractions in the activity front was 11.4 (10.9-11.6)/min at the proximal transducer. This new technique enables small-bowel motility to be monitored over longer periods of time and with much less inconvenience to the patient than previously used methods.