A six year old male cat with a history of three days' anorexia was presented for examination. He carried his head down on the left side, circled to the left, showed incoordination and displayed marked nystagmus. The right pupil was dilated; the left, constricted. Both pupils exhibited poor photomotor reflexes. Examination of the left external ear canal revealed inflammatory debris and elicited a severe pain reaction. Blood studies throughout the 8-day period showed a rising white blood cell count, with predominantly abnormal primitive granulocytic series cells in the peripheral blood and crowding out the normal bone marrow cells. Anaemia was also shown to be developing. The cat was given supportive and symptomatic therapy while in the clinic. Eight days following admission he died. Post mortem examination showed that the left tympanic bulla was softened and filled with purulent material, and that the 8th nerve was inflamed and hemorrhagic. The spleen was enlarged and the bone marrow showed termendous cellularity. Microscopic examination showed that the spleen, kidney cortex and portal areas of the liver had been infiltrated by leucocytes with abnormal nuclei; as had the circulatory systems of the liver, spleen, bone marrow and brain. These findings led to a diagnosis of myelogenous leukemia and an acute otitis media.