Severe, prolonged back pain was observed in 2 patients following lumbar artery embolization with Gelfoam for angiomatous spinal lesions. Dense, persistent staining of the paravertebral muscles with a characteristic striated pattern and elevated levels of creatine phosphokinase suggested muscle infarction and necrosis. Similar angiographic and laboratory findings were reproduced in monkeys following arterial embolization with Gelfoam.