Proliferative activity in the adrenal cortex of 10 days old chick was studied using autoradiographic technique with tritiated thymidine. The study provides an approximate distribution of DNA synthesizing and/or dividing cells in the chick adrenal cortex. The data indicate the presence of dividing cells both in the subcapsular zone (SCZ) and the inner zone (IZ) and their low or non-migratory activity within 360 hrs after injection of the isotope. This clearly suggests that both the SCZ and IZ are proliferative in chick adrenal.