We discontinued high-dose intravenous immunoglobulin treatment (IVIg) in 7 patients with chronic inflammatory demyelinating polyneuropathy (CIDP) who seemed to have responded to IVIg. After discontinuation of treatment, all 7 patients deteriorated. We then randomized the patients to IVIg or placebo (albumin) treatment in a double-blind crossover study. The clinical condition of all patients improved after IVIg and did not improve after placebo treatment. The mean time lapse from the end of the trial treatment to the occurrence of deterioration was 6.4 weeks after treatment with IVIg and 1.3 weeks after treatment with placebo. This selected group of patients with CIDP had a beneficial response to IVIg.