Lactating Holstein cows were assigned to clinical groups (CG; retained placenta, RP, n=20; uterine infection, UI, n=22; control, C, n=18) and given GnRH (200ug,im) or saline (T) on d 15 postpartum, to evaluate reproductive tract involution, uterine discharge, bacterial population and inflammation, ovarian activity, reproductive efficiency and plasma progesterone, glucose, and urea. Reproductive tract involution was not affected by CG or T and was complete by 40 d postpartum (DPP). Purulent vaginal discharge was found in UI, but improved over DPP. C, UI and RP had plasma progesterone concentrations > 1 ng/ml at 21, 27 and 29 DPP, respectively. Prolonged luteal phases resulted when UI was treated with GnRH. RP plasma urea was 20, 16.5 and 21.5 mg/100ml on 15, 35 and 50 DPP. UI had 16.3, 14.7 and 16.8 mg/100 ml on 15, 35 and 50 DPP. C and had 12.2, 14.3 and 12.8 mg urea/100ml on 15, 30 and 50 DPP. Plasma glucose ranged from 63 to 61.2 mg/100 ml between d 15 and 50. C. pyogenes and E. coli incidences were 53 and 22, 35 and 37, and 12 and 41% for RP, UI and C, respectively. Neutrophils were found in 58% of GnRH treated cows. Diffuse lymphocytes occurred in RP, 54%; UI, 40.5% and in C, only 5.4%. Days open were 134, 117 and 97 and services per conception were 2.5, 1.7 and 1.6 for RP, UI and C, respectively. RP and UI had increased time to plasma progesterone elevation, increased plasma urea concentration and increased days open. GnRH did not beneficially affect reproductive efficiency. / M.S.