Over a 21-year career in the unit, Doll rose to become its director. His research there initially focused on the role of occupational factors in causing peptic ulcers. In 1950, he undertook, with Austin Bradford Hill, a study of lung cancer patients in twenty London hospitals, at first under the belief that it was due to the new material tarmac, or motor car fumes, but rapidly discovering that tobacco smoking was the only factor they had in common. Doll himself stopped smoking as a result of his findings, published in the British Medical Journal in 1950, which concluded: Four years later, in 1954, the British doctors study, a study of some 40,000 doctors over 20 years, confirmed the suggestion, based on which the government issued advice that smoking and lung cancer rates were related. In 1955, Doll reported a case-controlled study that firmly established the relationship between asbestos and lung cancer. In 1966, Doll was elected to the Royal Society. The citation stated: In 1969, Doll moved to Oxford University, to sit as the Regius Professor of Medicine, succeeding the clinical researcher Sir George Pickering. Initially, epidemiology was held in low regard, but in his time at Oxford he helped reverse this. He was the primary agent behind the creation of Green College, which was founded in 1979. Doll was appointed the first Warden of Green College, whence he retired in 1983. Green College merged with Templeton College in 2008 to become Green Templeton College, which is located on the site that was previously Green College. Doll also helped found the National Blood Service, and was key in avoiding a system of paying donors for their blood, as had been adopted in the United States. His continued work into carcinogens at the Imperial Cancer Research Centre at the John Radcliffe Hospital, Oxford, working as part of the Clinical Trial Service Unit, notably including a study undertaken with Richard Peto, in which it was estimated that tobacco, along with infections and diet, caused three-quarters of all cancers, which was the basis of any of the World Health Organization's conclusions on environmental pollution and cancer. Doll was made a Fellow of the Royal Society (FRS) in 1966, knighted in 1971, and awarded the Edward Jenner Medal of the Royal Society of Medicine in 1981. Also in 1981, Doll became a founding member of the World Cultural Council. He was a member of