The effect of 2% cholesterol feeding on changes throughout postnatal development of total, free, and esterified cholesterol in neonatal chick liver and kidneys was studied. The increase observed in the hepatic cholesterol content after supplementation of the diet with 2% cholesterol was mainly due to the accumulation of esterified cholesterol. Small but significant differences were also found in the esterified cholesterol content in kidneys between control and cholesterol-fed animals. In normally fed chicks, the hepatic percentage of squalene synthesized from mevalonate decreased during the first days of independent life while cholesterol percentage increased. On the contrary, the percentage of squalene recovered in kidneys immediately after hatching was minimal, increasing during postnatal development. Addition of 2% cholesterol to the diet produced a clear inhibition in the mevalonate incorporation into nonsaponifiable lipids by liver slices, especially from 4 days onwards. This inhibition was particularly clear in the percentage of cholesterol synthesized. Mevalonate incorporation by kidney slices was higher than in liver, although cholesterol supplementation had little influence on the percentage of each nonsaponifiable lipid formed. In normally fed chicks, kidneys metabolized mevalonate by the shunt pathway not leading to sterols at a rate more than 50 times that of liver. Cholesterol feeding produced a clear enhancement of the hepatic shunt pathway while in kidneys it had practically no effect.