Dual isotope gastric emptying studies were performed on 16 morbidly obese patients before and after gastroplasty to determine the effect of this surgery on the rate of emptying. The solid and liquid phases of gastric emptying were compared with a normal control group. In the 900-g and 50-g meals there was a significant difference in the mean half emptying time between solid and liquid phases of emptying (p less than 0.05). Pre-operatively, the 900-g meal half emptying times of both solids and liquids and the 50-g liquid phase meal did not differ significantly between obese patients and the control group. However, in the solid phase of the 50-g meal obese patients differed significantly from a control group (p = 0.007). Three months after gastroplasty, gastric emptying of 50-g meals from the total stomach was not significantly changed from the pre-operative 50-g meal values in ten of 12 patients (p less than 0.05) and no change in total stomach emptying times were seen at 12 mo compared to the 3-mo study (p less than 0.05). Emptying of the pouch alone for both solids and liquids was significantly faster than the pre-operative and postoperative total stomach studies. Gastric emptying in the obese is normal with large meals, but is delayed in small meals. In most patients, gastroplasty does not result in slower emptying of meals.