A human pancreas-specific protein (PASP), previously characterized as a serum marker for acute pancreatitis and pancreatic graft rejection, has been identified as pancreatic procarboxypeptidase B (PCPB). cDNAs encoding PASP/PCPB were isolated from a human pancreas cDNA library using a combination of nucleic acid hybridization screening and immunoscreening with antisera raised against native PASP. The deduced amino acid sequence of PASP/PCPB cDNA predicts the translation of a 416-amino acid preproenzyme with a 15-amino acid signal/leader peptide and a 95-amino acid activation peptide. The proenzyme portion of this protein has 76% identity with rat PCPB and 84% identity with bovine carboxypeptidase B. DNA and RNA blot analyses indicate that human PCPB mRNA (1,400 nucleotides) is transcribed from a single locus in the human genome in a tissue-specific fashion. N-terminal sequencing of native PASP and the specific immunoreactivity of bacterially expressed PASP/PCPB with native PASP antibodies confirm the identification of PASP as human pancreatic PCPB.