Acute mastitis was consistently produced in primiparous ewes by inoculation of the mammary gland, via the teat canal, with an isolate of Pasteurella haemolytica, serotype A9, originating from a field case of ovine mastitis. Mastitis developed following the inoculation of as few as 10 colony forming units of this isolate, suggesting that only a small number of organisms would be required to initiate the disease under natural conditions provided they were already beyond the teat canal. Clinical signs and macroscopic lesions were well developed within 24 h of inoculation and were similar to those found in the naturally-occurring disease. The ability to reproduce mastitis consistently will facilitate studies of the pathogenesis of the disease and the comparison of different isolates of P. haemolytica with respect to virulence determinants.