An intravenous injection of 10 i.u. oxytocin into rams 10 min before ejaculation increased the number of spermatozoa per ejaculate by 45%. The optimum dose was between 5 and 10 i.u. oxytocin and the optimum interval between the injection of oxytocin and ejaculation was 5 to 10 min. The increase in the number of spermatozoa per ejaculate was accompanied by increases in semen volume, and/or sperm concentration. The increase in the semen volume and total fructose per ejaculate suggested that oxytocin stimulated the accessory sex glands. Adrenaline injections had no effect on the output of semen.