The pattern of gastric emptying in 15 obese patients and 11 control subjects has been assessed using a double isotope technique for measuring solid and liquid emptying with a scintillation camera. In all studies solid emptying was characterized by a lag period (before food enters the duodenum) followed by linear emptying. Liquid emptying was faster than solid and was non-linear. In obese patients solid emptying was delayed due to prolongation of the lag period, and the duration of the lag period correlated with excess body weight. There was no significant change in liquid emptying in obese patients. In control subjects no relationship between gastric emptying rates and body weight was apparent.