The two aims of these experiments were first, to examine the relationships between mean daily stool weight, mean weight per stool, frequency of defecation, dye transit time, dietary fiber intake, and transit time of small radiopaque pellets, and second, to determine the ability of these measures of bowel function, singly or in combination, to predict gastrointestinal transit time of the pellets. Variables were obsewrved simultaneously in 13 healthy women consuming controlled low and high cellulose diets. All except one of the correlation coefficients between the measures of bowel function were significant. Stepwise regression analysis retained log stool weight, fiber and dye transit to predict log of the mean transit time of all pellets (R2 = 71.3); the same three variables were selected to predict log of the transit time of 80% of the pellets (R2 = 59.4). Mean daily stool weight explained about 50% of the variation for both measures of transit, while dye transit and dietary fiber explained the rest. Log transformation of either stool weight or pellet transit time or both variables improved the prediction by about 10%. These results suggest that prediction of pellet gastrointestinal transit time from other measures of bowel function may be limited and is influenced significantly by the fiber level of the diet.