A feature of many B-cell tumors is a surface-expressed immunoglobulin (sIg). The complementarity determiningregions (CDRs)of the sIg， termed the 'idiotype'， are unique to each tumor. We report on a phage selection strategy to generate anti-idiotype therapeutics that react with sIg CDR3 sequences: the MEC1 B-cell tumor line was used as proof of concept.