The migrating motor complex (MMC) shows large variations within an individual and between individuals. This study aimed to investigate, with respect to this variability, the importance of gastric or duodenal origin of phase III activity. Interdigestive 6- to 10-h stationary antroduodenal motility recordings of 19 healthy male subjects were analyzed for MMC cycle durations and duration of phases I, II, and III, all with respect to the place of origin of each phase III. Data are given for the duodenal recording site as means ± SE. Mean MMC cycle duration was 117.3 ± 13.9 min, regardless of the place of origin of phase III. Seventy-two phase III cycles were observed in total, 35 and 37 starting in the "antrum" and duodenum, respectively. After a phase III of "antral" origin, MMC cycle duration was 156.1 ± 11.0 min, significantly longer than MMC cycle duration following a phase III of duodenal origin, 80.5 ± 10.7 min (P < 0.001). Phase III duration was longer when of "antral" origin than when starting in the duodenum (7.6 ± 0.4 and 5.3 ± 0.4 min, respectively; P < 0.001). MMC cycle duration and duration of phases I, II, and III depend on the place of origin of phase III ("antral" or duodenal) and on the origin of the preceding phase III. This factor explains part of the MMC variability observed within individuals. Mean MMC cycle duration in healthy subjects or patients should therefore also include information on the origin of phase III.