Complement fixation tests using threeB. ovisantigen preparations in warm fixation tests (WCFT) and cold fixation (CCFT) tests were done on 541 ram sera. Semen samples from the same rams were examined culturally to identifyB. ovisexcretors. The CCFT, using an antigen prepared by heat extraction ofB.oviscells, had a sensitivity of 97% in 124 rams which were sheddingB.ovis. The specificity was 99% in 144 rams from non-infected flocks. Seventy-seven per cent of 156 rams which reacted to this test were sheddingB. ovisin their semen. Tests with other antigens were inferior in sensitivity and/or specificity. The WCFT gave lower titres than CCFT. Vaccination caused large numbers of false positive reactions in 4 flocks.