P falciparum invasion efficient in normal RBCs of different densities. Normal RBCs from 4 different donors were harvested from the indicated arabinogalactan concentration ranges and used to sustain P falciparum cultures as described in “Materials and methods.” Parasite counts were assessed on Giemsa-stained blood smears after 38 hours of incubation of the culture. At least 1000 RBCs were counted per slide on 3 different slides. “All” indicates parasite counts in the original, unfractionated RBC samples. The columns and error bars report the means and SDs of the triplicate counts. Labels 1-4 in quadrants indicate a different donor.