A dual radioisotope technique was used to measure gastric emptying of a mixed solid and liquid meal in 30 obese (> 125% of ideal body weight) subjects and 23 age- and sex-matched nonobese control subjects. Gastroduodenal motility studies were also performed on seven obese and 10 nonobese subjects to compare postprandial antral motility. In addition, eight obese subjects underwent gastric emptying studies before and after substantial weight reduction (mean 8.3%). Gastric emptying of both solids and liquids was similar in obese and nonobese subjects, and antral motility indices did not differ between the groups. Gastric emptying rates before and after substantial weight reduction were similar. We conclude that neither gastric emptying nor antral motility appear to be abnormal in morbidly obese subjects; neither does gastric emptying appear to be affected by substantial acute weight reduction.