A study was made of the daily elimination of fetal neutral sterols in 22 healthy subjects and the average proportions of the main sterols were established. These were cholesterol (9.5%), its main bacterial transformation products: coprostanol (65%) and coprostanone (less than 6%), cholestanol (less than 2%), delta7-cholestenol (less than 2%) and phytosterols (18%). Epicoprostanol, which indicates a secondary mean of bacterial degradation of cholesterol has been searched for systematically. In general, traces only are present but in one case it amounts to more than 8% of the neutral sterols. The bulk of neutral sterols eliminated daily is very variable for different subjects and also for a same subject, although the concentration of fecal sterols is relatively constant (6.37 +/- 0.36 mg of sterols/g of feces). For a given subject under controlled diet conditions, differences in fecal elimination of sterols can essentially be ascribed to irregularity of digestive transit.