Leptospirosis associated with probable L. hardjo infection was investigated in a dairy herd in a coastal district of Western Victoria. Thirty-six of 110 cows suffered leptospiruria and mastitis characterised by flaccid udders and abnormal milk. One of two media used enabled the isolation of the organism from infected guinea pigs inoculated with fresh urine. Microscopic agglutination titres to L. hardjo were elevated during the outbreak. There was an associated human infection.
