Acute and chronic inflammatory demyelinating neuropathies are among the most common treatable neuropathies seen by neurologists. Evidence for effective therapy has only recently been provided by randomized or controlled trials. In the Guillain-Barré syndrome such evidence does not support the use of corticosteroids or immunosuppressive agents. However, when used early in the course, plasma exchange (PE) has been shown to lessen the severity and shorten the duration of the disease; it is indicated only in severely paralyzed patients or those whose rapid deterioration suggests the imminent need for ventilatory support. Some patients with chronic inflammatory demyelinating polyneuropathy (CIDP) respond to corticosteroid therapy or other immunosuppressive agents. PE is also effective in certain patients, but there is no sound evidence to date concerning combined immunosuppression and PE. The rationale of PE in these conditions and whether it is the removal of a toxic factor or the replacement fluid used that is beneficial remains to be clarified.