Factors influencing the density of stools from 33 healthy subjects (nine had floating and 24 sinking stools) and six patients with steatorrhea were investigated. All floating stools sank when their gas volume was compressed by positive pressure. Thus, to float, stools must contain gas. After degassing, previously floating and sinking stools had similar specific gravities, indicating that the floating or sinking propensity of such stools depends upon differences in gas rather than fat content. A high stool gas content (and hence a floating stool) in healthy subjects appeared related to colonic methane production. Steatorrheic stools had a relatively normal gas content. The density of their nongaseous fraction was less than normal, but resulted primarily from increased water rather than fat content. Thus, stools float because of an increased content of gas or water (or both); the floating stool should not be considered a sign of steatorrhea.