A panel of microcell hybrids containing fragments of chromosome 2 was analyzed for the presence of human DPP4, the gene that codes for dipeptidyl peptidase IV (or CD26), by specific PCR amplification of a fragment of the 3' untranslated region of the gene. This analysis placed DPP4 between LCT and GAD in bands q21 to q31. The localization was confirmed by in situ hybridization using two genomic probes that each revealed a hybridization signal in band q24. We also use the recent identification of the ADA binding protein as DPPIV to propose that the gene ADCP2 should be renamed DPP4.