Ten cows with and 5 cows without puerperal endometritis were treated with 20 μg GnRH analogue, buserelin, intramuscularly. Blood samples were taken every 20 min for 8h before and for 8h after injection of GnRH. All cows responded to GnRH with significant increase of LH 20 min after treatment. The LH peak was significantly lower in cows with puerperal endometritis than that in clinically normal cows (27.91 ± 5.47 ng/ml vs 80.60 ± 17.2 ng/ml; p ≤ 0.01). The total AUC of LH was also significantly smaller in cows with puerperal endometritis compared to cows without it (p ≤ 0,01). The results suggest that the delayed resumption of ovarian function in cows with uterine infection may be caused by reduced responsiveness of the pituitary to endogenous GnRH. Further studies are needed in order to investigate the mechanism of this phenomenon.