For determination of CoA, the method of Kaplan and Lipmann was used. The determinations of CoA were made on the liver, kidney and brain of rats ranging from the neonatal period to 40 days of age. The concentration of hepatic CoA was lower in neonatal period, thereafter, it gradually increased with growth and reached the constant level at 30 days after birth. In the kidney, the concentration of CoA was also lower in neonatal period, but it increased with the growth of rats by 10 days after birth. The brain CoA concentration approached to the adult level when rats were 20 days of age. The total content of CoA in the liver and kidney increased with the growth of rats from birth and in the brain it reached the constant level by the time rats were 20 days old.