This gene encodes a member of the carboxylesterase large family. The family members are responsible for the hydrolysis or transesterification of various xenobiotics, such as cocaine and heroin, and endogenous substrates with ester, thioester, or amide bonds. They may participate in fatty acyl and cholesterol ester metabolism, and may play a role in the blood-brain barrier system. The protein encoded by this gene is the major intestinal enzyme and functions in intestine drug clearance. The transcription of this gene is regulated by several factors including HNF-4alpha (hepatocyte nuclear factor-4alpha), Sp1 (specificity protein 1), Sp3 and USF1 (upstream stimulatory factor 1). The expression and activity of this gene is age-related but independent of growth hormone level. This gene is clustered with several family members including a few of pseudogenes and Ces5 on chromosome 8.