Born in Germany in 1875 he qualified from the Medical School at Freiburg in Baden in 1899 and soon afterwards emigrated to America. He was appointed to the staff of the Mount Sinai Hospital, New York, and eventually became consulting surgeon. He was instrumental with others in the great development of the Hospital during the fifty years in which he served it. He was also consulting surgeon to the Beth Israel Hospital. He was elected a Fellow of the American College of Surgeons in 1916, three years after its foundation, was a member of the American Gastro-enterological Association, and served on the American Board of Surgery, the official body for registration of surgical specialists. After Landsteiner's discovery of the blood groups in 1901 there was a wide-spread revival of interest in blood transfusion, and much thought was given to making it a safe procedure. Lewisohn was one of the three men, working quite independently, who announced the practicability of the sodium citrate method in 1914 and 1915. Lewisohn knew that sodium citrate was used to prevent clotting in specimens sent for pathologic investigation, and proved that it was safe for human blood transfusion in a concentration of 0.2% where a transfusion of 5g was not exceeded. Albert Hustin had already announced this method in Brussels on 6 April 1914, though he advocated mixing the citrated blood with glucose solution which diluted it too much. Luis Agote used the citrate method at Buenos Aires on 14 November 1914, and Lewisohn made his announcement in New York on 23 January 1915. General acceptance of the method followed his full paper in the issue for July 1915 of *Surgery, Gynecology and Obstetrics* (Chicago), which had a world-wide circulation. Although urgently needed during the great war which began in August 1914, the new method was introduced to the British Army medical services only late in 1917 by the Canadian surgeon Oswald Robertson. The American Association of Blood Banks awarded its Karl Landsteiner prize to Lewisohn in 1955. He was elected an Honorary Fellow of the College in 1959 and came to London at the age of 83 for his admission. He described his blood-transfusion method as "not in the least complicated or revolutionary". He died in New York on 11 August 1961 aged 86. Details of the Reports on Transfusion mentioned above: Albert Hustin. Note sur une nouvelle méthode de transfusion; communication préliminaire. *Bulletin de la Société royale des Sciences médicales, Bruxelles*, 6 April 1914, 72, 104-111. Principe d'une nouvelle méthode de transfusion muqueuse. *Journal de Médecine de Bruxelles*, 1914, 12, 436-439. Luis Agote. Nuevo procedimiento para la transfusion del sangre. *Anales del Instituto moderno de Clinica medica, Buenos Aires*, January 1915, 1, 25-30. Richard Lewisohn. A new and greatly simplified method of blood transfusion; a preliminary report. *Medical Record, New York*, 23 January 1915, 87, 141-142. Blood transfusion by the citrate method. *Surgery, Gynecology and Obstetrics, Chicago*, July 1915, 21, 37-47. Oswald H. Robertson. A method of citrated blood transfusion. *British medical Journal*, 27 April 1918, 1, 477-479.