Leeching is an art dating back at least to ancient Egypt. It reached its zenith in the late 18th and early 19th centuries. The antithrombotic quality of leech saliva was first noted by Haycraft in 1884 and the active anticoagulant ingredient isolated in 1904 by Jacoby. He gave this agent the name ‘hirudin’. Hirudin was isolated in pure crystalline form by Markwardt in 1957 and first produced in quantity by genetic engineering in 1986. The salivary glands of several species of leech also contain other biologically active substances which are currently undergoing investigat