Eight cats and one dog with signs of cervical ventroflexion, reluctance to walk, a stiff and stilted gait and muscle weakness are introduced. Though blood potassium concentration was very low (< 3.0 mval/l) in one cat and the dog only, a potassium depletion myopathy was assumed as the cause of these symptoms. Two of three cats had elevated values of the urinary fractional potassium excretion compared to ten healthy cats. Blood creatinine values were within normal ranges. Five of seven cats had elevated creatine kinase values. All animals improved after potassium substitution. Causes of potassium depletion are discussed and differential diagnoses of myopathies are briefly mentioned.