The use of orally administered choline chloride in the treatment of cerebellar and spinocerebellar ataxia was investigated by a short-term double-blind crossover trial in 20 patients with ataxia. These patients, who include 7 with Friedreich's ataxia, 7 with mixed spinocerebellar ataxia and 6 will primary cerebellar degeneration received placebo and 6g/day or 12g/day of choline with crossover at 6 weeks. Serum choline levels were measured 1 h after the first daily dose. Mild but significant improvement in upper limb co-ordination was noted in 3 patients with Friedreich's ataxia, 3 with mixed ataxia and 4 patients with primary cerebellar degeneration. Improvement in gait and lower limb co-ordination was observed in only 2 patients (one with cerebellar ataxia and 1 with mixed ataxia) There was no correlation between serum choline levels and clinical response to choline. Choline chloride produces a mild but functionally significant improvement in motor co-ordination in some patients with cerebellar and spinocerebellar ataxia.