Premature oviposition of hard-shelled eggs was effected in the hen by intraven. inj. of pitressin or pitocin. Pitressin in doses of 0.0625 to 0.25 vasopressor units and pitocin in doses of 0.625 to 2.50 oxytocic units gave yields of approx. 30 to 90%. % yields over these ranges following injs. of pitressin and pitocin were proportional to the logarithm of vasopressin content, although equivalent yields required slightly less than twice the dose in pitressin as in pitocin. In terms of the commonly assumed composition of pitressin and pitocin, 0.1 unit of vasopressin +0.005 unit of oxytocin was approx. equivalent to 0.05 unit of vasopressin +1.00 unit of oxytocin. Premature oviposition can apparently be effected by vasopressin alone, but oxytocin in sufficiently high cones, also contributes to the reaction.