The concept of chemical neurotransmission arose from detailed studies on the functioning of the autonomic nervous system, particularly those of T. R. Elliott, H. H. Dale and Otto Loewi during the first three decades of the 20th century. This paper will assess some of their contributions, and discuss the relevance of earlier work, especially that of W. H. Gaskell and J. N. Langley, on the anatomy and physiology of the autonomic nervous system. Emphasis is given to the work that Dale and his colleagues performed on the elucidation of acetylcholine as a normal constituent of the mammalian body, and subsequently as a probable chemical neurotransmitter in the parasympathetic nervous system, at other autonomic sites and at the voluntary neuromuscular junction.