Sir Henry Hallett Dale was an English pharmacologist and physiologist. For his study of acetylcholine as agent in the chemical transmission of nerve pulses (neurotransmission) he shared the 1936 Nobel Prize in Physiology or Medicine with Otto Loewi.

Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Parts in the body that use or are affected by acetylcholine are referred to as cholinergic.