We conducted a double-blind, placebo-controlled study in 13 patients (aged 22 to 54 years) with relapsing-remitting multiple sclerosis (MS). They were randomly assigned to receive a loading dose of immunoglobulin IgG, 0.4 g/kg body weight/day for 5 consecutive days, followed by single booster doses of 0.4 g/kg/day, or placebo, once a month for 9 months. MRI was obtained before and during the 3rd and 6th months of treatment; examinations in the 9th and 12th months were planned. Qualitative and quantitative blinded assessments were performed. There were seven patients who received active treatment and six who received placebo. Statistical analysis was performed by the Wilcoxon test. A decrease in the size and number of lesions was observed on MRI in five patients (71%) in the treatment group, and in two (33%) of the placebo group at 3-month follow-up. At 6 months follow-up MRI, a decrease in the amount of lesions was observed in all patients treated with i.v. IgG, and in two (33%) of the placebo group; four patients (66%) receiving placebo showed an increase. Quantitative analysis showed a statistically significant decrease in the volume of lesions in treatment group at both 3 and 6 month follow-up. There was no statistically significant change in the placebo group.