Esterases are a large group of enzymes found in plasma (or serum) and tissues, which hydrolyse a number of xenobiotics. Some of these enzymes have not yet been measured in tropical domestic animals. In the present work, we have measured the activities of three esterases, viz. aspirin esterase, cholinesterase and nitrophenylacetate esterase in the plasma and livers of male and female camels, cattle, sheep and goats. The results indicate that the enzyme activities are highest in the goat, followed by sheep and cattle (which showed broadly similar activities), and lowest in camels. Gender had no statistically significant effect, although males exhibited about 5-8% more enzyme activity in each of the four species, than females.