Auditory brainstem responses (ABR) were investigated in 26 patients with acrodermatitis chronic atrophicans, which is a late manifestation of Lyme borreliosis. Nine of the patients showed pathological ABR, four of them unilaterally and five bilaterally. The main pathological findings were: 1) Poor reproducibility of waves IV-V or of wave V; 2) Increased latency of wave V. After antibiotic treatment, ABR was improved in eight of the nine patients, and in three of them it was normal. In the five patients who did not completely recover, the improvement consisted in better reproducibility and a tendency towards normal wave V latencies. The results of this study indicate that the central nervous system may become involved in patients with acrodermatitis chronica atrophicans.