What was Erwin Chargaff's discovery?

In 1950 Erwin Chargaff, who was a leader in the field of biochemistry, discovered that the chemical units of DNA, known as "bases," always occurred in pairs. Chargaff's work lead directly to the discovery of the double-helix structure of DNA, by James Watson and Francis Crick, in 1953.

Although Watson and Crick cited Chargiff for their Nobel Prize-winning discovery, Chargaff would never be rewarded for his efforts. Later in his life he became openly critical of scientists, who worked in the field of molecular biology, stating that they were involved in "the practice of biochemistry without a licence." He died on June 20, 2002, at the age of 96.