Liver amylase activity in rodents was assayed with Blue Starch as substrate, and found to be higher than in humans or pigs. Based on the result of concanavalin A affinity chromatography, we found that the sugar moieties of amylase molecules increased in parallel with amylase activity in the tested mammals. However, the amounts of amylase proteins determined by Western bloting with anti-human salivary-type antibody as the probe, were similar to the levels in mammalian livers. Moreover, a similar expression of amylase mRNA was also detected in the mammalian livers by a reverse transcriptional-polymerase chain reaction using primers specific for the human salivary and/or pancreatic amylase complementary DNA (cDNA) sequences. The amylase was detected at the catalytic activity, protein molecule and mRNA levels in rat liver at all ages from fetus to adult. Salivary-type liver amylase activity increased up to one week after birth, and was maintained at the adult level thereafter. However, based on the results of the electrophoretic mobility test, livers with accelerated amylase activity, e.g., at 2-4 weeks after birth or during liver regeneration after partial hepatectomy, were also found to express an amylase electrophoretical identical to pancreatic-type amylase in addition to salivary-type activity. These results suggest that the liver may express an etopic amylase in a certain condition.