In the two past years 25 patients with generalized myasthenia gravis (MG) were treated with high-dose intravenous immunoglobulin G (IVIG) at the Institute of Neurology in Belgrade. The patients were affected with severe forms of MG (IIB, III and IV according to Osserman's classification) refractory to all previous treatment. All patients received IVIG, 250-350 mg/kg during five consecutive days. An immediate positive effect was mild and recorded 12-15 days later in only 37.5% patients. On the contrary, 92% patients showed delayed improvement which was effective for over six months. Distribution and severety of the disease decreased as expressed by reduced Besinger mean clinical score from 12.3 to 5.7 after six months. Immunologic parameters before and after IVIG treatment did not differ significantly. An increase of IgG was observed in 88% of patients. IVIG side effects were infrequent, usually mild, and qualitatively different from those induced by other therapies (azathioprine, corticosteroids). The authors emphasize the beneficial delayed effect of IVIG on the course of MG which resulted in significant reduction of the dose of additional immunosuppressive agents. The absance of immediate therapeutic effect of IVIG does not justify this mode of treatment in acute deterioration and crisis of MG.