The inoculation of 2000 colony-forming units of Corynebacterium pseudotuberculosis into one teat canal of each of three cows resulted in severe, chronic, pyogranulomatous mastitis. Within three days the cows had a reduced haematocrit, haemoglobin concentration and red cell count. The anaemia was initially normocytic, normochromic and non-regenerative, and was associated with a brief peak of neutrophilia; a regenerative response became evident two to three weeks later. Clinical signs of mastitis appeared seven to 14 days after the inoculation, with a peak of high fever, more severe anaemia, a second peak of neutrophilia and the complete cessation of milk production from all quarters; extensive and severe pyogranulomatous mastitis developed in the inoculated quarters. No other lesions were detected postmortem, and C pseudotuberculosis was cultured from the affected quarters but not from the supramammary lymph nodes and viscera.