The effect of forced molt on pituitary function and other endocrine parameters was investigated in three year old hens subjected to a dietary forced molting procedure. In addition to molting, fasting caused cessation of egg production, body and organ weight loss, alterations in hormone secretion and morphological changes in some endocrine glands. Body and ovary weights decreased but returned to normal with ad libitum feeding. Pituitary, thyroid and adrenal weights were not affected but serum hormone levels measured by RIA revealed a decrease in LH, FSH and PRL and increases in TSH, T₃ and GH all of which returned to higher levels with ad libitum feeding. Serum P₄ levels remained low (and egg-laying stopped) until ad libitum feeding was resumed and then increased and egg-laying returned to a typically productive level. Serum ACTH and T₄ increased with fasting and remained elevated. Gonadotrophs and corticotrophs increased in numbers with fasting and/or food restriction but thyrotrophs, somatotrophs and lactotrophs decreased. Correlations between cell populations and serum hormone levels was quite common. Colloid-filled follicles resembling a hypertrophic thyroid gland occurred throughout the pituitary pars distalis. Granules appear to be discharged into the follicular lumen through exocytotic pores in the apical plasmalemma of follicular cells. Lactotrophs, corticotrophs and somatotrophs are commonly arranged in follicles or clusters. PRL-containing granules are in the center of some follicles and are concentrated near pituitary cysts. Pituitary cysts, lined with ciliated epithelium and sparse mucous cells, are more prevalent in fasted hens and decline with the resumption of feeding. Reduced lactotroph populations and presumptively degenerated lactotrophs in cyst lumens are correlated with reduced serum PRL levels. Necrotic cells occurred in the pituitary parenchyma of fasted birds but dilated RER in the thyrotrophs of fasted hens indicate enhanced activity of these cells. Ultrastructural evidence presented here indicates that pituitary secretion by lactotrophs occurs both intraluminally and perivascularly.