Alternatives to high dose benzylpenicillin treatment are sought for in patients with mild Borrelia burgdorferi nervous system infection. Doxycycline 100 mg twice daily for 10-20 days was used in nine patients with radicular pains, vertigo or weakness in the legs caused by B. burgdorferi infection. The patients had suffered from neurologic symptoms for a median time of five months. In eight patients doxycycline was orally administered and in one intravenously. All nine patients had remission of radicular pain and vertigo during the treatment period. Two patients with weakness in the legs improved slowly in muscle strength over a three month period. The doxycycline concentration in the cerebrospinal fluid was 0.2-1.0 mg/l and in serum 1.9-7.1 mg/l after five days treatment. Doxycycline treatment was found successful in our patients with mild tick borne neuroborreliosis.