The use of the hormones, diethylstilboestrol, hexoestrol and testosterone propionate, as growth stimulants in beef cattle has been studied. The subcutaneous implantation of 60 mg. stilboestrol into steers fattening in yards produced a highly significant increase in rate of gain (65%) and little difference in the yield and quality of the carcass. The implantation of 24 nig. or 36 mg. of diethylstilboestrol or 30 mg. hexoestrol into Friesian bullocks fattening on pasture produced highly significant increases in rates of gain (29%, 48% and 33% respectively). No significant difference was found in the rates of gain produced by these three treatments.