Injection of tungstic acid gel (but not pH adjusted saline) into the cat lumbar ventral horn results in spontaneous, epileptiform activity consisting of waves of repetitive, high frequency, action potentials in motoneurons surrounding the injection site. In most motoneurons the action potentials are grouped in high frequency bursts composed of action potentials triggered from the delayed depolarization of the preceding action potential. The same kind of bursting can be triggered by intracellular current pulses, indicating that altered neuronal membrane properties are associated with the bursting activity. This type of bursting differs markedly from that seen in motoneurons during penicillin or strychnine-induced spinal seizures.