Bilateral hindlimb paresis occurred in 3 guinea pigs after immunization with an adjuvant-antigen mixture containing complete Freund's adjuvant. Doses were injected into unanaesthetized animals, divided among 3 or 4 sites, and given slightly off midline in the subcutaneous tissues of the back. Neurologic examination of affected animals revealed intact flexor and panniculus responses and limited voluntary movement of the hindlimbs. Histopathologic interpretation of 2 affected animals showed fibrogranulomatous material effacing the skeletal muscle and vertebral bone, with marked bone lysis and infiltration into the marrow space and spinal canal. In addition, multiple granulomas in the pulmonary parenchyma were noted. A postmortem radiograph of the excised thoracolumbar spine of 1 animal revealed a soft tissue swelling and "moth-eaten" and geographic osteolysis of 2 spinous processes. Hindlimb paresis and osteolysis likely resulted from accidental injection of the adjuvant-antigen mixture into the epaxial musculature and subsequent extension of injection site granulomas into the spinal canal.