Skin test antigens for the diagnosis of brucellosis were produced from the roughBrucellu abortusstrain 45/20. The production of two products termed Brucellin B and Brucellin W are described. The method described for the production of Brucellin W is recommended as an improved practical method of Brucellin production. The Brucellin products described were equal in sensitivity to that of a commercially available product, Brucellergen, which is used in New Zealand. Brucellin B was extensively tested in non-infected cattle and its specificity was equal to that of Brucellergen. Recommendations for the standardisation of skin test reagents for the diagnosis of brucellosis are made. Intradermal testing for brucellosis in cattle should be used only for the identification of infected herds and not as an individual animal test.