A complementary DNA encoding a new bovine tryptase isoform (here named BLT) was cloned and sequenced from lung tissue. Analysis of sequence indicates the pres-ence of a 26-amino acid prepro-sequence and a 245 amino acid catalytic domain. It contains six different residues when compared with the previously characterized tryptase from bovine liver capsule (BLCT), with the most signifi-cant difference residing at the primary specificity S1 pocket.