A new approach was taken to isolate a full-length cDNA encoding the gamma-subunit of nerve growth factor (NGF). An oligonucleotide probe was used first to identify kallikrein-related sequences in a cDNA library derived from male mouse submaxillary gland mRNA. Of 10,000 clones, 860 were identified as being kallikrein-related; these were analyzed further by hybridization to synthetic oligonucleotides using a procedure which eliminates the effects of base composition and thus allows distinction between partial and perfect sequence complementarity. Nine clones hybridized with a gamma-subunit-specific probe at high stringency, and the nucleotide sequence of the longest cDNA insert was determined. Regions of homology and variability within the kallikrein gene family are maintained in this protein and probably reflect the similar functions and different substrates for this family of proteins.