The efficacy of Brucella melitensis strain Rev. 1 vaccine against a Brucella ovis experimental infection was judged on 30 rams, 15 of which had received 8.5 X 10(8) Rev. 1 at the age of 4 months. All were challenged 9 months later by conjunctival route with 5 X 10(8) B. ovis. The 30 rams were killed three months after challenge and were autopsied. Genital and other organs and lymph-nodes were searched for B. ovis. Only a few organs and lymph-nodes of three vaccinated rams shed B. ovis, contrary to controls which were all heavily infected. The distribution of infection indicated that the most frequently infected organs are the vesicular glands which, more than epididymes, seem to be the target organs of the infection. These results show that immunization with strain Rev. 1 is very effective against B. ovis infection. It is recommended to vaccinate rams of four to six months in an area where B. ovis or B. melitensis infection, or both, are prevalent.