Abstract
One hundred IU of corticotrophin causes premature ovulation in the laying hen. The effect is not due to LH contamination. Corticosterone at levels of 0.5, 1.0 and 5.0 mg/hen does not induce or block ovulation. Ten mg corticosterone/ hen causes blocked as well as premature ovulations whereas 20 mg/hen consistently blocks spontaneous as well as progesterone-induced ovulation if given one hour prior to the progesterone. The same level of corticosterone fails to block progesterone-induced ovulations if given simultaneously with the progesterone. The possible mechanisms involved in these phenomena are discussed.