Trager, W., Gill, G. S., Lawrence, C., and Nagel, R. L. 1999.Plasmodium falciparum: Enhanced gametocyte formationin vitroin-reticulocyte-rich blood.Experimental Parasitology91,115–118. Concentrates of late stage parasites of the gametocyte-forming clone HB-3 were mixed with blood rich in reticulocytes from anemic patients, or with normal control blood, and kept under culture conditions for 4 days. Significantly more gametocytes were always formed in the reticulocyte-rich blood than in the control. This was true whether the anemic blood supported a larger asexual parasitemia than the control, or a lower one, or the same and without regard to the cause of the anemia. Gametocytes as a percentage of asexual forms were up to 10 times higher in reticulocyte-rich blood than in normal blood.