The results of a controlled trial in which 38 patients with severe acute inflammatory polyradiculoneuropathy took part indicate that plasma exchange favourably influenced the course of the disease. Significant benefits were seen in time until onset of improvement, course of muscular weakness, improvement in disability grades over the first 2 months, and working capacity after 1 month. Cost-benefit analysis showed that the exchange treatment resulted in net financial savings. The results suggest that plasma exchange may have a role in the treatment of severe acute inflammatory polyradiculoneuropathy.