Polymyositis (PM) and dermatomyositis (DM) are dysimmune diseases usually treated with corticosteroids and immunosuppressants. Human polyvalent immunoglobulins administered intravenously (IgIV) are known to be effective in some dysimmune diseases. Between August 1987 and September 1989 we conducted an open trial of IgIV in 15 patients (mean age 44 +/- 14 years) with either PM (12 cases) or DM (3 cases) associated with a collagen disease in 2 patients. In 14 of these 15 patients the conventional treatments (corticosteroids, immunosuppressants, plasmapheresis, total body irradiation, lymphopheresis) had failed. One patient was seropositive for picornavirus and received IgIV as initial treatment. IgIV infusions were given 4 +/- 3.9 years on average after the onset of PM or DM. Twelve of the 15 patients received another treatment, starting at least 6 weeks before IgIV and pursued without dosage increase, which consisted of corticosteroids (11 cases), methotrexate (5 cases) or plasmapheresis (1 case). Human polyvalent immunoglobulins for intravenous use were prescribed in doses of 2 g/kg/monthly course. All but two patients (1 course) received 3 to 6 courses on average. The IgIV infusions were well tolerated in 12 patients; 3 patients showed allergic manifestations which regressed. Therapeutic effectiveness was evaluated by muscle testing and by repeated assays of creatine phosphokinase (CPK). Clinical improvement, usually perceptible after the first course, was observed in 13/15 patients; it was associated with a more than 30 percent decrease of the initial CPK level in 13 patients and with a reduction of associated therapies in 9 patients. In the entire patient population a statistically significant lowering of mean CPK value was observed as early as in the first course (P less than 0.001). In view of their effectiveness, rapid action and safety, intravenous Ig infusions may be regarded as an interesting treatment in PM or DM patients.