In a 2 x 2 factorial experiment fertility has been compared after insemination on observed oestrus, and insemination on a time basis. It was done on 10-day intervals. A group of progestagen sponge (MAP) treated ewes was compared following insemination at observed oestrus and insemination at a predetermined time. The prostaglandin treated group was inseminated at 60 and 72 hours following the last injection of cloprostenol and the sponge treated group at 48 and 60 hours following sponge withdrawal. Although the conception rates of ewes averaged 12,75% less following fixed time A.1. as compared to A.1. at observed oestrus (64,0% vs 50,0% for the sponge group and 65,4% vs 53,9% for the prostaglandin group, respectively ), these differences were not significant. Keywords: Synchronisation. oestrus, sheep. A.I. by oestrus or time