CDNA clones for human kallikrein have been identified in a cDNA library constructed from mRNA of human salivary gland. The entire coding sequence for preprokallikrein and for the 5'- and 3'-untranslated regions were isolated by using a mixture of oligonucleotides corresponding to amino acids 51-56 of human urinary kallikrein and one oligonucleotide corresponding to amino acids 233-238 of human pancreatic kallikrein. The DNA sequence proved that, with the exception of two amino acid exchanges, kallikrein of the human salivary gland is identical with pancreatic kallikrein. Salivary gland and renal kallikrein was expressed in Escherichia coli from plasmid pKK223-3 under the control of the tac promoter. The protein was identified by Western-blot analysis and by demonstration of its specific proteolytic activity.