To obtain information on possible determinants of weight loss after horizontal gastroplasty, pouch emptying was prospectively investigated in 27 morbidly obese patients. A scintigraphic method was used. Examinations were carried out every 6 months until 2 years after surgery. Pouch emptying was described by means of delay, time until half emptying, mean transit time, and emptying rate. The measures all showed a significant (p less than 0.05) acceleration of pouch emptying during the first 6 months after gastroplasty. Thereafter pouch emptying was unaltered. No significant association could be detected between measures of pouch emptying and weight loss. From calculation of 95% confidence intervals for coefficients of correlation it proved very unlikely that pouch emptying is an important determinant of weight loss.