Over a period of 10 days, 17 dogs became weak and developed neurological deficits of different degrees of severity. About 12 hours before these clinical signs appeared they had all eaten a particular brand of commercial dog food from a recently opened bag. They were all quadriparetic and hyporeflexic, and some of them also showed additional systemic or neurological signs, including dyspnoea, a high body temperature, tongue laxity, hyperaesthesia and anisochoria. Serum biochemical abnormalities included high activities of creatine kinase, lactate dehydrogenase and aspartate aminotransferase. Analysis of the suspect food revealed high concentrations of the ionophore lasalocid. Fifteen of the dogs were given supportive treatment at home and two were hospitalised. Five of the dogs died, but the others improved gradually and had fully recovered by one to four days after the appearance of the clinical signs.