In two herds of sheep with numerous abortions Campylobacter fetus subspecies intestinalis was isolated from fetuses, fetal membranes, and faecal specimens. In herd A, with good hygiene, 12 ewes out of 250 aborted. In herd B, with poor hygiene, 54 out of 171 ewes aborted and 14 of them died; for a further 9 ewes the lambs died postnatally. The clinical course in both herds shows that proper supervision and possibilities of prompt isolation of aborting ewes can substantially reduce the spread of infection within the herd. The isolated strains of C. fetus subsp. intestinalis were catalase-positive, did not grow in deep culture on 0.5% semisolid agar, reduced nitrate, did not grow in 3,5% NaCl, but grew in 1% ox bile and 1% glycine. All the strains were negative with respect to H2S production on TSI but positive on lead-acetate strips. In serological tests, positive agglutination titres were demonstrated only in aborting ewes from herd B. Positive titres were also demonstrated in a ram from the same herd.