Chloroquine dose-response curve. Chloroquine responses of P. falciparum in erythrocyte cultures obtained using PG (A) and SGI (B), after removal of haemoglobin/detergents. Sigmoid graphs show the survival of P. falciparum Dd2 at different concentrations of drug. Bars indicate the standard errors of the mean for two independently processed samples. The calculated IC50 values were 136.2 ± 28 nM for PG and 118 ± 15 nM for SGI.