Three domestic short-haired cats with a history of anorexia and loss of body condition had high rectal temperatures, and a normocytic, normochromic anaemia. Two of them were also dyspnoeic, and thoracic radiographs revealed a diffuse, unstructured increase in radio-opacity involving all the lung lobes. Examination of Giemsa-stained blood smears and culture of blood monocytes revealed purplish-staining intracytoplasmic inclusions, in monocytes and lymphocytes, which occurred either singly or in aggregates. Electron micrographs of a buffy coat smear from one of the cats revealed round intracytoplasmic inclusions, with electron dense and lucid areas morphometrically similar to those found in other members of the genus Ehrlichia. An attempt to culture chlamydia from one of the cats was unsuccessful. The cats were treated successfully, one with tetracycline hydrochloride and the other two with imidocarb dipropionate.

Clinical, haematological, biochemical, electrophysiological and pathological features of two dogs infected with Ehrlichia canis and with concurrent signs of polymyositis are presented. Both dogs had a history of relatively acute onset, progressive tetraparesis, hyporeflexia and generalised muscle wasting. Skeletal muscles were atrophic and characterised histologically by plasmocytic, lymphocytic and immature lymph‐oreticular cellular infiltrates with accompanying areas of necrosis. Histopathological similarities between ehrlichiosis and polymyositis are noted and a probable aetiological relationship is inferred.

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Pulmonary arterial disease was produced by the placement of flexible polyvinyl chloride threads (similar in size, shape and flexibility to adult female Dirofilaria immitis) in the pulmonary arteries of dogs. Several different types of pathological change were apparent ranging from subendothelial oedema and endothelial loss, mild intimal proliferation and thrombus formation to organised fibrous encasement of the threads in areas where they had become impacted in the lumen of the artery. This range of pathological changes is very similar to that produced by D immitis and suggests that the intima of the canine pulmonary artery may react to different insults in a similar way.

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