Résumé : Rahnella aquatilis, a bacterium whose natural habitat is water, is exceptionnally mentioned in human pathology. A strain of this species was isolated several times from the sputum of a patient with chronic lymphatic leukemia. The clinical observation as wall as the bacteriological findings are reported in this present note. The identification of this «new Enterobacteriaceae is at present facilitated by the use of the Api 20E system. © 1987.