Two patients with chronic hepatitis B received adenine arabinoside, at a dosage of 1000 mg/d for 8 weeks and 700 mg/d for 12 weeks, respectively. At the end of the treatment period both patients had developed severe sensory irritability in the distal parts of the legs: perception of all sensory modalities was impaired. The disorder persisted over the following three years, although in a milder form. Shortly after the onset of the symptoms sensory nerve conduction velocity in both lower legs was not definitely impaired. But six months later it was clearly reduced to below 40 m/sec in the sural nerve, a finding which has persisted a year later. Three years after the first examination both patients are slightly improved, but conduction velocity is not yet normal. The objectively demonstrated long course and the considerable subjective complaints associated with the polyneuropathy argue for a very therapeutic use of adenine arabinoside.