ABSTRACT:The effect of age upon iron retention in cockerels of laying and meat type hybrids was examined within 46 subsequent balance periods. Chickens were fed ad libitum a diet with the content of 312 mg Fe per 1 kg. The dependence of Fe utilisation upon age from Day 3 to Day 100 was expressed by the second degree parabolas with minimum values in the tenth week of age. The dependence of Fe content in weight gains on age was highly significant (P < 0.01). The course of this dependence was expressed by parabolas with minimum values on Day 38 and Day 28 in slow and fast growing chickens, resp. The growth rate of total amount of Fe in the body was by 6 per cent lower (P < 0.01) than that of live weight of chickens.