Replacement therapy with intravenous immunoglobulin (IVIG) is currently the therapy of choice in patients with antibody-formation deficiency. Our 30-month experience with IVIG treatment in 8 patients with common variable immunodeficiency and in 4 patients with x-linked agammaglobulinemia previously treated by intramuscular immunoglobulin or low-dose IVIG is presented. Long-term dosage was 400 mg/kg once in 3--4 weeks. Ten patients reported an improvement of their health state, especially the signs of their chronic bronchitis improved. Compared to 2 cases of pneumonia which occurred within 30 months before IVIG therapy had started, no case of pneumonia occurred during IVIG treatment. Infusion rate of 4 mg/kg/min was safe enough in 11 of our patients. Serum trough IgG level is the most important for laboratory monitoring of the patients under IVIG therapy.