Patients with Roux-en-Y anastomoses may have chronic symptoms of nausea, vomiting, epigastric fullness, and abdominal pain. To investigate the mechanism of these symptoms, the electrical activity of the Roux limb was studied in five symptomatic and four asymptomatic patients with Roux-en-Y anastomoses. Slow-wave and spike activity in the Roux limb were recorded using six bipolar suction electrodes positioned 10 cm apart. Ten healthy volunteers were studied as a control. In the control subjects, the mean slow-wave frequency decreased from 11.27 +/- 0.2 cycles/min at 30 cm below the ligament of Treitz to 10.96 +/- 0.2 cycles/min at 80 cm past Treitz. By contrast, in five patients the slow-wave frequency in the Roux limb increased from 11.12 +/- 0.2 cycles/min 10 cm below the gastrojejunal anastomosis to 11.42 +/- 0.4 cycles/min 50 cm more distally. Four of these five patients had severe symptoms. In the other four patients, of whom three were completely symptom-free, an aborally decreasing slow-wave frequency was observed. In both the controls and the patients with Roux-en-Y anastomoses, the direction of propagation of phase 3 spike bursts of the migrating motor complex was always aboral. During phase 2, most spike bursts were uncoordinated at adjacent recording sites. Propagated spike bursts, single or repetitive, were rare. The propagation direction of these spike bursts was always aboral in healthy controls. In symptomatic patients with inverted slow wave frequency gradients, however, the rare propagated spike bursts always propagated orally. The observed electrical abnormalities may in part be responsible for the symptoms of patients with the Roux-en-Y syndrome.