Chymase is responsible for the formation of angiotensin II, which plays crucial roles in the pathogenesis of cardiovascular diseases. In the present study we determined the gene organization of a novel hamster chymase (hamster chymase 2) and analysed the expression of chymase 1, chymase 2 and angiotensin-converting enzyme (ACE) in hamster hearts at the terminal stage of cardiomyopathy. The gene encoding hamster chymase 2 is 3.2 kb in length and has five exons and four intervening sequences. The overall organization of this gene is similar to that of several other serine proteases. The deduced amino acid sequence revealed the existence of a preproenzyme composed of a signal peptide with 19 amino acids, a propeptide with two amino acids and a catalytic domain with 226 amino acids. The predicted full sequence of the catalytic domain was revealed to be very similar to the sequences of mouse mast-cell protease 5 (86%), rat mast-cell protease III (85%) and human chymase (70%) and less similar to hamster chymase 1 (56%). The expression of chymase 1 in heart was higher than that of chymase 2. The cardiac chymase-like activity, as well as the mRNA levels of chymase 1 and 2 of BIO 14.6 cardiomyopathic hamsters at the age of 60 weeks were increased 3.4-, 2.8- and 5.1-fold respectively compared with age-matched BIO F1B control hamsters. The cardiac ACE activity and the ACE mRNA level of cardiomyopathic hamsters were also increased 4.1- and 2.4-fold compared with those of age-matched controls. These results suggest that up-regulation of both ACE and chymases participates in the pathophysiology of the terminal stage of cardiomyopathy.