Immunization using a combination of Id/GM-CSF fusion protein and CpG ODN enhances production of antigen-specific IgG. Mice were immunized with 50 μg of Id/GM-CSF as a single subcutaneous dose with or without CpG ODN. 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. (A) Anti-Id response was measured at various time points after immunization. (○) Id-KLH; (•) Id-KLH; (▵) Id/GM-CSF; (▴) Id/GM-CSF + CpG ODN. (B) Anti-Id response was measured 4 weeks after immunization with various doses of Id/GM-CSF. (▨) Control CpG ODN; (▪) CpG ODN.