We treated 17 patients with chronic inflammatory polyneuropathy (CIP) with infusions of fresh-frozen plasma (FFP). Thirteen patients had a beneficial response: 12 improved considerably and one moderately. The first signs of improvement were seen within 8 days of the onset of treatment. None of these patients had had spontaneous remissions for 2 months prior to treatment, and none had received immunosuppressive medication during the plasma infusions. The treatment effect was short-lasting in 9 patients. Re-institution of the FFP infusions was always followed by improvement. The same effect could be achieved by intravenous gamma-globulin. We conclude that infusions with FFP, of which the IgG fraction is the effective part, may induce a rapid and clinically important improvement in patients with CIP.