Synchronization of oestrus has been used to increase reproductive efficiency in most animals, including ewes. The aim of the present study was to compare the effect of the length of a progestagen treatment (12 d vs. 6 d) on synchronization efficiency (oestrus response, time to onset of oestrus and duration of oestrus) and fertility rate using fluorogestone acetate (FGA) progestagen sponge treatment with pregnant mare serum gonadotropin (PMSG) administration applied at different times of sponge removal. Ewes (n = 68) were divided into two groups; long term (LT, n = 33) and short term (ST, n = 35) groups treated with FGA progestagen sponges. At the end of intravaginal sponge treatment period the animals of each group were divided into the 3 subgroups in relation to time of PMSG (300 IU) treatment. PMSG treatment was applied 24 h before sponge removal, at sponge removal and 24 h after sponge removal for LT I and ST 1, LT2 and ST2, and LT3 and ST3, respectively. Each ewe was inseminated intra-cervically twice with skim cow milk-diluted semen (1000 x 101 motile cells/ml) 40 It and 60 h after sponge removal. Non-return rates (NRR-30) were monitored from 12 day after sponge removal to 30 day with the aid of teaser rams. Onsets of oestrus response and oestrus cessation were significantly different (P < 0.05) between the ST and LT treatment groups. Synchronization of oestrus was tighter in LT than ST group. Except for oestrus cessation, other indicators studied were not different in the ST subgroups. In the ST subgroups the oestrus cessation of the STI (88.7 +/- 15.4 h) was the shortest and differed from ST3 (120.0 +/- 14.2 h) (P < 0.05). No statistical difference was observed among all studied indicators for LT groups according to application time of PMSG (P > 0.05). The NRR-30 and lambing rate of the ST and LT after timed AI were 35.7% and 31.0% and 32.1% and 28.6%, respectively (P > 0.05).