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Levels of luteinizing hormone (LH), prolactin, progesterone, cortisol, estrone and estradiol-17~ were determined during the postpartum anestrous period in samples collected from six second-calf, crossbred, suckled beef cows. Blood samples were collected at 6-h intervals beginning 2 wk before expected parturition and continuing until 10 d after first postpartum estrus. Samples were also collected at 15-rain intervals for 4 h once weekly. The postpartum interval was 48 + 19 d (mean + SE). Serum progesterone levels fell from a mean of 2.1 +-1.2 ng/ml 2 d prepartum to basal levels of .1 + .1 ng/mt 6 d postpartum and remained at this level until just before estrus. An elevation (1.3 + .1 ng/ml) in serum levels of progesterone beginning 4.6 + .1 d and ending .6 + .1 d before estrus was observed in four cows. Mean levels of estradiol-17/3 in serum were 113 +-54 pg/ml at parturition and declined rapidly to 7-+ 3 pg/ml 6 d postpartum. Estradiol-17/3 concentrations remained at these levels until they ini Research supported in part by CSRS Grant #WS-999 "Reproductive Endocrinology of the Postpartum, Suckled Beef Female" (T.G.D.). The research is a contribution to regional research project W-112 "Reproductive Performance of Domestic Ruminants." 2Div. Anim. Sci.,