Human plasma carboxypeptidase B (CPB2) is a recently described carboxypeptidase, first isolated on the basis of its ability to bind plasminogen (4). Although the normal function of this protein is not well understood, it has several characteristics that suggest that it plays a role quite different from that of the known pancreatic carboxypeptidase B (CPB1)(1). We undertook a study to map the CPB2 gene and to compare its chromosomal location to that of other carboxypeptidases. We used NIGMS hybrid cell mapping panel 2 in our study (3). This mapping panel contains 24 hybrid cell lines. In most cases these lines contain a single human chromosome on the rodent background, which is either mouse or hamster. We used PCR to determine the presence of the plasma carboxypeptidase B gene in the~ cell lines. We used PCR primers with the following sequences: primer PBP. PCR. 13