Clinical examinations and nerve biopsies were performed on four patients with meningoradiculoneuritis and positive serology for Borrelia (Garin-Bujadoux-Bannwarth syndrome). Three patients had a painful multiplex mononeuropathy, while one presented with a picture resembling a Guillain-Barré syndrome. Nerve biopsy in two patients revealed marked perivasculitis, in part with thrombosis of the epineural vasa nervorum. In the other two patients there were small pericapillary infiltrates in the endoneurium with strikingly many plasma cells. These findings speak, on the one hand, for angiopathic-ischaemic nerve damage, but on the other for a local immune reaction to the causative microorganism, because of the plasma-rich endoneural infiltrates. The authors suggest that angiopathic-ischaemic tissue lesions and/or local immune reactions may play a role also in the pathogenesis of CNS complications of Lyme disease.