Serum levels of prolactin (PRL), luteinizing hormone (LH), progesterone and estradiol-17β were compared in female turkeys during various phases of their reproductive life cycle. Prolactin levels of broody turkeys were higher (2164 ± 127 ng/ml) than those of laying turkeys (468 ± 74 ng/ml), which were in turn higher than those of hens that had stopped laying (119 ± 18 ng/ml). Serum LH, progesterone, and estradiol-17β levels of laying hens were significantly higher than those of the other two groups. The levels of these hormones did not differ between broody hens and hens that had stopped laying, but were not broody (photorefractory hens). Serum prolactin levels of broody hens dropped markedly within a day of nest-deprivation and confinement to cages. Levels remained low while hens were in cages. When nests were again made available to broody hens that had been deprived of nests for 48 h, they resumed nesting within 5 min, and serum prolactin levels then increased. In other experiments, it was found that a significant decline in serum prolactin occurred after 8, but not 4 h of nest-deprivation. After a 48 h period of cage confinement of hens, prolactin levels were seen to increase within 30 min after hens were returned to their home pens. Levels continued to rise and had nearly reached pre-cage confinement levels by 12 h after resumption of nesting.