A chymotrypsin-like protease was purified to homogeneity from human tonsils by a series of chromatographic procedures. The purified enzyme gave a single protein band with an apparent molecular mass of 30 kDa on SDS-PAGE. The sequence of the first 21 amino acids at the N-terminus of the enzyme was determined. A cDNA for the enzyme was cloned by PCR amplification from extracted tonsillar mRNA using a supposed N-terminal oligonucleotide primer and a conserved C-terminal primer of the chymase family. The deduced amino acid sequence of the isolated clone was identical to that of human chymase in connective tissue-type mast cells from heart except for a Ser instead of a Cys at the N-terminal 7th position.