There is a hepatitis of dogs which occurs in acute, persistent and chronic forms. Histological studies of spontaneous cases suggested that several apparently diverse hepatic diseases might be stages of one process. This was also implied by follow up studies and case histories: acute non-lethal episodes were followed later by the development of chronic hepatitis, cirrhosis and liver failure. Serum was taken and homogenates of liver were made from three field cases representing different putative temporal stages of the complex. These were injected into experimental dogs and a hepatitis was induced in all. The cytopathological and histological changes were the same in all animals and were identical to field cases. Acute lethal disease and persistent infections were produced. Two second passages were carried out and an identical condition was induced, characterised by recurrent episodes of subclinical hepatitis and persistent infection. It is suggested that the disease might be named canine acidophil cell hepatitis in view of the pathognomonic cytopathology. Specific morphological criteria have been established for this hepatitis.