Ammonium perchlorate (thyroid depressant) and catosal (organic phosphorus preparation mixed with vitamin B, Bayer Co.) were added to the basal ration of 596 one-day-old Fayoumi chicks till the age of 16 weeks. A significant increase was observed in the live body weight, paired testes weight, sperm per gramme tissue and total sperm per testes in group receiving annonium perchlo rate at levels 25, 50, 100, 200 and 400 mg per kg ration and Catosal at alevel of 3 ml per litre drinking water for 16 weeks. Variations in the level of blood serum urea non-protein nitrogen and total cholesterol of certain groups did not have any deleterious effect on the health of such growing chicks when both compounds were added.