Previous studies have shown that i.v. endotoxin infusion causes gastrointestinal dysfunction and intestinal injury in piglets. The aim of this study was to investigate the effects of endotoxin on intestinal myoelectric activity in newborn swine and to correlate this with gastrointestinal and hemodynamic events. Three pairs of electrodes were implanted in the jejunal wall of piglets, and after recovery, intestinal myoelectric activity was continuously recorded in the conscious, fasted condition. The intestinal myoelectric activity on the control day showed regular, repeating migrating myoelectric complex (MMC) cycles, each of which was composed of the classic phases I, II, and III. Mean cycle duration was 67.0 ± 18.7 min (±SD), and phase III comprised 9.1 ± 2.2% of each cycle. On the next day, infusion of 30 μg/kg endotoxin caused an initial, prolonged quiescent period and delayed the appearance of the first posten-dotoxin phase III complex. After the quiescent period, there was a period of irregular spiking activity followed by several shortened MMC cycles (47.9 ± 22.7 min, p < 0.01 versus control) with a prolongation of the percentage of time spent in phase III (15.4 ± 11.3%, p < 0.01). Endotoxin thus produced biphasic alterations in intestinal myoelectric activity characterized by an initial quiescence followed by increased gastrointestinal smooth muscle activity. Animals developed diarrhea, hypotension, and tachycardia about 1 h after endotoxin infusion in temporal association with increased spiking activity and MMC cycling. These studies are the first to show this biphasic response to endotoxin.