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Secretory patterns of serum tri-iodothyronine, thyroxin and testosterone were analysed by specific radioimmunoassay in Kaghani (n= 42), Rambouilet (n= 42) and Kaghani Rambouillet (n= 42) male sheep to determine age and breed related changes. Animals were examined at 1-2 wk, 8, 10, 12, 20, 22 and 24 months of age (n= 6/age group). All animals were maintained under standard conditions of feeding and management. and concentrations were maximal (p< 0.01) in 1-2 wk old lambs of all breeds studied ( and , respectively). For all the breeds, concentrations of declined markedly (p< 0.01) at 8 month of age and then varied in a narrow range () up to the age of 24 month. While, serum concentrations decreased (p< 0.01) to nadir () at 10 months of age in all the 3 breeds. Afterwards, levels increased gradually and attained a small peak at 20 months before declining again at 22 and 24 months of age. Serum and concentrations were correlated significantly (p< 0.05) and their ratio was constant at all ages in the different breeds. Age significantly (p< 0.01) influenced the secretion of testosterone in the breeds examined but the breed differences were comparable. Mean serum concentrations of testosterone were low from 1-2 wk to 10 months of age in the Kaghani, Rambouillet and Kaghani Rambouillet animals. Peak testosterone levels were noted in the 12 months old Kaghani (), Rambouillet () and their cross animals (). Mean testosterone levels, thereafter, decreased at 20 months and then at 22 and 24 …