Four patients are presented who exhibited progressive muscular rigidity in both legs, the thoracolumbar, paraspinal and the abdominal muscles. In only one patient, there was an initial involvement of the shoulder girdle muscles. Electromyography in all four patients at rest recorded continuous electric activity resembling an interference pattern. Following sudden exteroceptive stimuli the activity increased in amplitude and density this corresponded clinically to painful spasms. All patients had oligoclonal banding in CSF. In the serum and CSF of three patients IgG subtype autoantibodies were detected. These have been found to be directed against GABAergic nerve terminals in the rat and human cerebellum and, more specifically, to glutamic acid decarboxylase. All patients improved on clonazepam. Trials of intermittent high-dose methylprednisolone administration gave relief from rigidity in one patient and permitted reduction of clonazepam in another. Intravenous immunoglobulins however had no effect in one patient.