Two groups of castrated male adult goats (three goats/group) were infected intravenously with the Ball 3 vaccine strain of Cowdria ruminantium and treated with long-acting oxytetracycline at the onset of clinical disease 10 days later. Five weeks post-vaccination one group was challenged with a Caribbean isolate (Gardel) and the other group with a West African isolate (Mali) of C. ruminantium. Non-vaccinated controls infected with either the Gardel or Mali isolate died. All of the vaccinated animals challenged with the Gardel strain reacted and survived. The three vaccinated animals challenged with the Mali isolate also reacted and two died of heartwater.