This study aimed to determine the best vehicle and administration route for progesterone administration in sheep. In a first replicate, single intramuscular doses of 25mg progesterone were administered to ewes previously ovariectomized, either in propylene glycol (group IM-PG, n=6) or olive oil (group IM-OO, n=5). In a second replicate, the same solutions of progesterone were administered subcutaneously to the same ewes (groups SC-PG, n=6, and SC-OO, n=5). In the present study, the best pharmacokinetic results of a single dose of 25mg of progesterone were obtained, both using PG and OO as vehicles, by the subcutaneous route. Thus, progesterone remained in plasma for a longer time after subcutaneous administration in PG than in OO (t(1/2beta): 60.65+/-13.07 vs. 27.51+/-3.59 h; P<0.05); the mean residence time being higher in SC-PG than in SC-OO group (88.99+/-18.36 vs. 41.04+/-5.31h; P<0.05). However, both vehicles allowed maintained plasma levels 0.5 ng/ml for at least 30 h, so any of these treatments may be efficiently used for administration of exogenous progesterone.