Repeated immunizations with a combination of Id/GM-CSF fusion protein and CpG ODN induce high levels of antigen-specific IgG. Mice were immunized with 50 μg of Id/GM-CSF as a subcutaneous dose with or without CpG ODN on week 0 and again on week 2. Blood was obtained weekly, and serum was evaluated for the presence of anti-Id IgG by ELISA. Normal mouse serum supplemented with a known concentration of monoclonal anti-Id was used as a standard. Three mice were included in each group. (○) Id-KLH; (•) Id-KLH + CpG ODN; (▵) Id/GM-CSF; (▴) Id/GM-CSF + CpG ODN.