The influence on transit time exerted by the density or diameter of pellets has been established in six ileostomy subjects. An increase in density from 1.0 to 1.6 significantly increased the average transit time of pellets in the small intestine. The average transit time for the light and heavy pellets being 7 and 25 h respectively. The diameter of pellets is of minor significance. The findings suggest the use of density as a means of modifying the period of absorption of controlled-release pellets.