Therapeutic plasma exchanges (PE) represent a new approach to the management of numerous immune diseases and are in full development. In practice, however, they require sophisticated equipment, heavy investments and fully trained staff, and they are not as free from dangers as was initially assumed. A rational appraisal of the results therefore is desirable, but prospective comparative studies are scarce, and the present indication all too often rest upon non-scientific criteria, such as the need to slow down the course of an allegedly severe disease or the subjective impressions of the therapeutic team. In spite of these uncertainties, it would seem that PE deserves a major place in the treatment of diseases due to auto-antibodies or circulating immune complexes, as well as in that of malignant monoclonal gammapathies with hyperviscosity of the blood, some acute or chronic metabolic disorders and occasional intoxications with substances highly bound to serum proteins, which constitute the usual indications. The indications proposed in this review paper are based on the most representative publications in this particular field and on the own experience of the authors, who have performed 1200 PEs between 1978 and 1980.