Serum antibodies to Borrelia burgdorferi antigen were determined in 71 consecutive patients with an acute peripheral facial palsy. The study was conducted for one year in a south western coastal region in Sweden. Twenty-one per cent of the patients had significantly elevated serum levels of antibodies to Borrelia burgdorferi antigen. CSF was examined in 13 of the sero-positive patients. In three of these (23%) Borrelia antibodies were found. Another five patients had a pathological protein and cell pattern in the CSF. No seasonal differences were observed. Four of the sero-positive patients had a long-term history of dermatological neurological manifestations compatible with the late third stage of the disease.