Pharmacology started to develop into a real quantitative science in 1909, when A.V. Hill derived the Langmuir equation in the course of his studies on nicotine and curare. A history of the developments since then shows both brilliant insights and missed opportunities. It also shows that much remains to be done. There is still no mathematical description that can describe quantitatively the actions of agonists on G-protein-coupled receptors, although progress has been greater with agonist-activated ion channels, which are much simpler.