The characteristics of meal-induced gallbladder emptying in healthy individuals are subject to wide variation. We hypothesized that some of the observed variation might relate to ingestion of the meal during different phases of the migrating motor complex (MMC). Recording of gastrointestinal pressure was combined with scintigraphic recording of bile kinetics during infusion of 99mTc-HIDA. The material consisted of 12 healthy men. Group 1 (n = 6) had a fat-rich meal in phase I, and group 2 (n = 6) had the meal in a phase II. With the end of the meal ingestion as zero, the following results emerged. The subjects in group 1 had a median (range) lag period before beginning of gallbladder emptying of 13.5 (9.0-22.5) min. In group 2 gallbladder emptying began during the meal ingestion in four subjects, and the median lag period was 0 min (minimum, -9.0; maximum, 13.5 (p = 0.02)). The median percentage change of gallbladder counts during the observation period of 54 min in group 1 was 11.5% (from 19% filling to 25% emptying). The corresponding figures in group 2 were 41% (from 2% to 91% emptying (p less than 0.05)). This difference was due to the difference in duration of lag periods, as the emptying rates measured from the end of the lag periods were equal. In conclusion, the onset of postprandial gallbladder emptying relates to the phase activity of the MMC at the time of ingestion.