The main purpose of plasma exchange is to remove toxic substances. The mechanisms involved appear to be complex. The primary aim of immunoglobulins is to compensate for immunodeficiency, but when given intravenously at high doses, immunoglobulins can also have unexpected immunomodulation effects. Routine therapeutic use of these methods raises the problem of cost and potential morbidity. Two therapeutic trials have demonstrated that plasma exchange in Guillain-Barré syndrome improves outcome when given early. In chronic polyradiculonevritis, plasma exchange and intravenous immunoglobulins have been shown to be equally effective although plasma exchange would give less satisfactory results in patients with polyradiculonevritis and monoclonal IgG. The effect of intravenous immunoglobulins is being evaluated. Plasma exchange has become the gold standard for acute crisis of myasthenia gravis. Recent results suggest that intravenous immunoglobulins could be equally effective in these diseases. Though useful therapeutic tools, the respective indications and optimal doses for these methods remains to be defined.