The aim of this study was to investigate the effect of PGF2α analogues and GnRH in cows, which had no spontaneous oestrus at 55-65"1 days postpartum, on oestrus, serum estradiol 17 p and pregnancy rates. The study was conducted in the Trakia Region on a total of 88 Holstein cows aged between 3-8 years and had no spontaneous oestrus in 55 days postpartum. The cows were separated into two groups (I. group n=46. II. group n=42). 0.5 mg cloprostenol was administered twice with 11 days interval to the I. group by [,M route. After coming to heat, the cows (n=44) of the first group were divided into two sub-groups. One of these sub-groups received 2.5 ml GnRH (Reccptal® Topkim) after the second cloprostenol and artificial insemination. Cows in the second group were treated with 25 mg Dinoprost by I.M route with 11 days interval. Like the first group these cows (n=39) also were divided into two sub-groups and one received a GnRH (Reccptal® Topkim) injection following artificial insemination. All cows in the first and second groups were inseminated artificially on 72nd and 96th hours following the second prostaglandin injections. Daily blood samples were collected from cows in both groups from the PGF2a administration day to 96th hour after administration, in order to determine serum estrogen levels. Highest scrum estrogen level was observed on the 3rd day after PGF2a administration in both (I. and II. groups) groups. Pregnancy was achieved in 32 of 46 cows (69.6%) in the first group and in 29 of 42 cows (64.1 %) in the second group. In the first group. 11 (50%), of 22 cows which had received GnRH after being inseminated conceived in the first cycle and other 8 conceived in the second cycle (36.4%). Eight of the cows which had not received GnRH conceived in the first cycle (n=22. 36.4%) and 5 (22.7%) cows conceived in the second cycle. In the second group 10 of 20 cows (n=20. 50%). which had received GnRH after being inseminated conceived in the first cycle and 6 (30%) conceived in the second cycle. Eight of the cows which had not received GnRH (n-19.42.1%) conceived in the first cycle and 5 (26.3%) in the second cycle. Administration of PGF2α analogues introduced for induction of oestrus cycles and ovarium activities in postpartum anoestrus events, made no improvement in oestrus and pregnancy rates. However, administration of GnRH together with prostaglandins makes a positive effect on the number of inseminations per pregnancy and pregnancy rates.