A comparative study was made of the serological response of rams to an inactivated Brucella ovis saline in-oil vaccine administered either once or twice by either the subcutaneous or the intraperitoneal route. The serological response of rams to two spaced doses of vaccine was more consistent and more persistent than when a single dose of vaccine was used. The rise in titre was more rapid and the final titre of greater magnitude when the subcutaneous route of administration was used in comparison with the intraperitoneal route. On a serological basis, the most satisfactory vaccination technique investigated consisted of two subcutaneous injections of vaccine administered ten weeks apart. The least satisfactory technique was a single intraperitoneal injection.