Abstract An inhibitor of cholesterol biosynthesis, 20,25-diaza-cholesterol (azasterol), was fed to male and female weanling rats in cholesterol-free diets containing 2, 5, or 30% corn oil, with or without added cholesterol. Growth and gross appearance were observed. Analyses were made of serum, liver, and carcass sterols. Rats receiving azasterol without added cholesterol exhibited growth retardation, alopecia, dermatitis, and achromotricia, and had high levels of desmosterol in serum, liver, and carcass. Increasing severity of the symptoms was as follows: males fed 30% corn oil 8 weeks, females fed 30% corn oil 9 weeks, females fed 2% corn oil 8 weeks, females fed 5% corn oil 15 weeks. Feeding cholesterol with azasterol delayed onset of gross symptoms in females, but not in males; tissue total sterols were similar to controls in all groups with moderate accumulation of desmosterol. It is concluded that feeding 0.03% of 20,25-diaza-cholesterol had deleterious effects on weanling rats. Gross symptoms appeared to be related to accumulation of desmosterol. The severity of the effects was influenced by sex and concentration of corn oil in the diet.