Blood neutrophil kinetics were studied withwith DF³²P in patients with sickle cell anemia. Neutrophil concentration in venous blood samples and the size of the circulating granulocyte pool (CGP) were high normal or abnormally high in all patients. The total blood granulocyte pool (TBGP) was not increased to the same degree as the CGP so that in part, the neutrophilia associated with sickle cell anemia represents a shift from marginated to circulating blood compartments. The half disappearance time (T½) of blood neutrophils tended to be short so that with an elevated or high normal TBGP the absolute granulocyte turnover rate (GTR) tended to be increased. The fractional GTR was regularly increased. In most types of neutrophilia the T½ tends to be increased rather than shortened and the fractional GTR may be normal, decreased, or increased. The increased fractional GTR observed in sickle cell anemia suggests that the absolute increase in neutrophil loss from the blood is not merely a function of increased pool size as was suggested previouslyy.