The aim of the present paper was to investigate the efficiency of different progestagen treatment methods in combination with Pregnant Mare Serum Gonadotrophin (PMSG) in Merino ewes outside the breeding season. A total of 78 ewes (2 to 4 years old) with a mean bodyweight of 58.4 kg and an average body condition score (BCS) of 3.5 were used in the trial. The ewes were randomly divided into 3 equal groups [n= 26]. Intravaginal progestagen sponges containing Fluorogestone Acetate (FGA; 30 mg) were inserted intravaginally for different periods (7_days: short-term; 10_days: mid-term, 14_days: long-term). In all cases, 500 IU PMSG was administered intramuscularly at sponge withdrawal. The oestrus response, lambing rate, multiple birth rate, fecundity and litter size were [65.4, 61.5, 18.8%, 0.77 and 1.25] in the short-term group; 80.8, 88.5, 34.8%, 1.31 and 1.48 in the mid-term group; and 96.2, 92.3, 62.5%, 1.50 and 1.63 in the long-term group, respectively. Oestrus manifestation and multiple birth rate were greater in long-term than in mid- and short-term groups, whereas for lambing rate, fecundity and litter size, better results were obtained in long- and mid-term than in short-term protocol. In conclusion, in Merino ewes, oestrus synchronisation outside the breeding season with long and mid-term progestagen treatment was found to be more effective than short-term treatment. [ABSTRACT FROM AUTHOR]