Abstract6 patients with myasthenia gravis (MG) underwent 26 plasma exchanges (PE) using fresh‐frozen plasma (FFP) as replacement solution. After each procedure, complement C3 conversion products (C3c) were detected in the plasma of all the patients. 3 patients had one or more attacks of urticaria during or immediately after the procedure. Using 5% albumin‐saline solution as plasma replacement solution, complement activation and urticarial reactions were not seen. It is concluded that infusion of FFP to patients with MG should be avoided as it may induce complement activation and allergic reacti