Bestatin is a dipeptide antitumor antibiotic. It shows no inhibition against aminopeptidase A, trypsin, chymotrypsin, elastase, papain, pepsin or themolysin. Activates macrophages and T lymphocytes and also has antitumor properties. It binds to cell surfaces and is an inhibitor for aminopeptidase B and leucine aminopeptidase.