The dose-response curve of P. falciparum anti-malarial drug susceptibility. Parasites were incubated with A) quinine without 'immune' plasma (white circle) and quinine with 10% 'immune' plasma (black circle) (range: 7.80-500 ng/ml); and B) artesunate without 'immune' plasma (white square) and artesunate with 10% 'immune' plasma (black square) (range: 0.16-10 ng/ml). The percentage of 3H-hypoxanthine uptake was plotted against drug concentrations. The dotted lines represent 50% and 90% inhibition. Data are shown as the median values and interquartile ranges from 4 experiments.