SUMMARY The effect of adrenaline on the normal milk-ejection response of the lactating sow to oxytocin has been examined for a limited range of concentrations. Both the duration of ejection and the change in intramammary pressure have been used as measures of the responses produced. The effects of 0·5 i.u. of oxytocin may be suppressed by 200 μg of adrenaline injected just before the oxytocin. This inhibiting action decreases as the period between the injections increases until after about 2 min the response is normal.