1. The characters of twenty-seven strains isolated from sheep in New Zealand and Australia were examined and compared with those of representative strains of Brucella abortus, Br. suis and Br. melitensis.
2. These strains could be classified in the brucella genus on the basis of cell morphology and staining, colonial morphology, cultural characteristics, biochemical properties, pathogenicity for laboratory animals and association with genital disease in the natural host.
3. The ovine strains have never been observed in other than the non-smooth phase. Consequently, these organisms lack the specific surface antigens of smooth brucellae but are antigenically closely related to the non-smooth variants of other brucella species. Three antigenic factors were identified and their presence confirmed in all twenty-seven ovine strains.
4. The N.Z. and Australian ovine strains appear sufficiently stable and distinguishable from other established groups of the brucella genus in a number of independently variable characters to justify their constituting either a new species, Brucella ovis, or a new variety, Brucella brucei var. ovis australasiae. The author wishes to thank Prof. W. I. B. Beveridge for his continued interest and for providing accommodation and facilities.