Parasite recovery from a 6-hour drug exposure. Plasmodium falciparum 3D7 parasite cultures were incubated for 6 hours with 100 nM chloroquine, 10 mM DFMO, 100 nM mefloquine, 100 nM artemisinin, 100 μM ritonavir or 0.1 nM gramicidin. The infected erythrocytes were washed and returned to culture in drug-free medium for an additional 48 hours, after which pLDH activity was determined for each culture (solid bars). Percentage parasite viability was calculated from pLDH activity relative to solvent-treated controls after subtraction of background values obtained with uninfected control erythrocyte cultures. Each drug treatment was performed in three parallel cultures and the bars represent the mean percentage parasite viability values and the error bars standard deviation.