Although the cause of most bovine mastitis can be attributed to the major pathogens of the udder (Staphylococcusspp.,Streptococcusspp. andEscherichia coli), occasional cases occur that are caused by more unusual organisms. The mastitis caused by a number of these organisms may be characterised by a very marked degree of tissue damage and, consequently, grossly abnormal mammary secretions. Notable amongst such organisms isBacillus cereus, for which a number of cases have been reported from many countries with significant dairy industries (Scheiferet al., 1976; Jones and Turnbull, 1981). In a British survey,B. cereusmastitis accounted for 0.3% of cases (Johnson, 1986), whilst in the Sydney region of Australia, 119 cows were diagnosed withB. cereusmastitis between 1960 and 1985 (Johnson, 1986). However, no previous case reports have been found for cattle in New Zealand, although it is isolated from time to time in routine culture of milk from cows with inexplicably high somatic cell counts (Anon, 1982; Graham, 1998). Only a very few cases have been reported from pastoral cattle anywhere in the world.