Leonard Colebrook's work was chiefly concerned with the control of the spread of infection in hospitals and the treatment of infected wounds. During the First World War he worked in Boulogne with Sir Almroth Wright, and advocated using the patient's inborn resistance to fight infection in wounds, using hypertonics rather than antiseptics which he argued were too harmful to the patient's tissues. In 1930 he was appointed to Queen Charlotte's Hospital where he developed the use of sulphonamides in the treatment of puerperal sepsis. In 1939, as bacteriologist to the Army in France, Colebrook introduced the dusting of wounds with sulphonamide powder, which greatly reduced the incidence of sepsis. In 1940 he joined an MRC team working on septicity of burns and scalds, and in 1943 went on to organise the burns unit at the Birmingham Accident Hospital, creating special dressing rooms with filtered air and near sterile conditions. After his marriage in 1946 he and his wife, Vera, embarked on a campaign leading to the passage of the Fireguards Act in 1952, and continued to campaign for non-flammable night clothing. In 1954 Colebrook's biography of Almroth Wright was published.