Crohn's disease is a disease with unknown etiology of which immunological mechanisms participate. As standard treatment is sometimes ineffective, in 15 patients therapeutic plasmapheresis was used. Before plasmapheresis and immediately after it some immunological parameters were assessed. In the serum a significant drop of all immunoglobulins of the basic classes was recorded: (P less than 0.05) and of circulating immunocomplexes (P less than 0.02). Marked clinical improvement was observed in three patients, which as compared with data in the literature, is somewhat less. The cause is in the author's opinion in the selection of patients (plasmapheresis is usually most successful in patients with marked activity of the disease and non-intestinal symptoms) even in case of less active plasma exchange. Despite this plasmapheresis can be recommended in patients with a poor response to common conservative treatment and in some of them we may expect a marked therapeutic effect with a favourable influence on the prognosis of the disease.