In a prospective study from 1983 through 1984, 77 patients (31 men and 46 women with a mean age of 47 +/- 20 years) with peripheral facial palsy of primarily unknown etiology were investigated. Only 2 patients with acute otitis media received antibiotics. Serology of the patients was investigated on days 1 and 14. IgG and IgM antibodies against herpes simplex, varicella-zoster and cytomegalovirus were determined by enzyme immunoassay, and against Epstein-Barr virus by immunofluorescence. In a retrospective analysis, IgM, IgA and IgG antibodies against Borrelia burgdorferi were determined by enzyme immunoassay. Borreliosis was diagnosed in 5 patients and varicella-zoster infection in 7. There was no statistically significant difference in recovery time between the different groups. Follow-up time for the patients with borreliosis was over 5 years. Neither meningeal symptoms nor polyneuropathy was observed in the patients with borreliosis even in the absence of antibiotic therapy.