U.S. biochemist, who discovered the chemical means by which acid–base (acid–base reaction) equilibria are maintained in nature.

Henderson spent most of his career at Harvard Medical School (1904–42), where he was professor of biological chemistry (1919–34) and chemistry (1934–42). Soon after his arrival there he began investigating how acid–base neutrality is maintained in body fluids. He found that the formation of carbonic acid from carbon dioxide and water in the presence of the salt of the acid (bicarbonates) is the only naturally occurring system, with the exception of phosphate solutions, that maintains a neutral acid-base equilibrium. Chemical systems of this sort, which maintain a specific acid-base equilibrium in body fluids, despite the addition of acids or bases resulting from physiological processes, are known as physiological buffers (buffer). The chemical expression developed by Henderson, and modified by the Danish biochemist Karl Hasselbach, to describe these systems, now known as the Henderson-Hasselbach equation, is of fundamental importance to biochemistry.

Henderson wrote two philosophical works, The Fitness of the Environment (1913) and The Order of Nature (1917), in which he argued that the planet's natural environment is perfectly suited for the development of life. Furthermore, he felt that “unique physical properties of matter” made a steadily increasing variety of chemical interactions inevitable; thus, chemical evolution, the creation of life, and biological evolution proceed by design and not accidentally. Henderson also wrote Blood, A Study in General Physiology (1928).