The aim of this randomized, double-blind, placebo-controlled cross-over study was to test whether valproic acid relieves painful polyneuropathy. Thirty-one patients completed two treatment phases of 4 weeks' duration with valproic acid (1,500 mg daily) and placebo. There was no significant difference between valproic acid and placebo in the rating of total pain (median, 5 in the valproic acid period vs 6 in the placebo period; p = 0.24) or in individual pain ratings.