The effect of pregnenolone, progesterone, deoxycorticosterone or corticosterone on the time of ovulation and oviposition in the hen.

Pregnenolone, progesterone, deoxycorticosterone and corticosterone were injected into hens between 16.30 and 17.00 h on the day of oviposition of the last egg of a sequence. 2. Pregnenolone did not affect ovulation, but all of the other steroids induced ovulation prematurely. 3. To induce premature ovulation in 50% of the hens, 82-31 mug+/-0-06 mug, 23-86 mug+/-0-07 mug and 659-26 mug+/-0-05 mug of progesterone, deoxycorticosterone and corticosterone, respectively were required for injection. 4. Differences were observed in the times of oviposition of eggs which ovulated in response to injections of either progesterone or a corticosteroid and it was suggested that the mechanism of action of progesterone and corticosteroids operates through different endocrine pathways.