We studied the mechanism of gastric emptying of a pH-sensitive radiotelemetry capsule with respect to phases of the interdigestive migrating motor complex (IMMC) in fasting normal volunteers and the effect of the Heidelberg capsule (HC) on the duration or timing of the IMMC phases. A manometric catheter with eight mounted solid-state strain gauges was passed transnasally and positioned fluoroscopically in the duodenum and jejunum in four normal, fasted male volunteers, in their right lateral position. The HC was administered orally following the establishment of one complete IMMC cycle (defined by the recording time between the end of two subsequent phase III activity fronts) and during the beginning of Phase I of the next cycle. The gastric residence time (GRT) of the HC was measured as the time of a gastric pH rise of greater than or equal to 3.0 units. In three subjects, GRT of the HC lasted to within 5 min of the onset of the next duodenal phase III of the IMMC, while in the fourth subject, the HC passed during the second phase III activity front. There were no significant differences in the duration of each phase of duodenal IMMC in the presence or absence of the HC (Phase I, 54 +/- 9.3 vs 31.6 +/- 10.1; Phase II, 22 +/- 8.1 vs 58.9 +/- 32; Phase III, 5.3 +/- 0.7 vs 4.2 +/- 0.7 min; mean +/- SE; P greater than 0.1 in all phases). In addition, the HC had no effect on motility index or patterns of contractions.(ABSTRACT TRUNCATED AT 250 WORDS)