Inhibiton Assay: For studying inhibition of Plasmodium or human DHODH enzyme, two assays that are in routine use are described, for example, in Baldwin, et al. (2002) JBiol Chem., 277, 41827-41834, and Baldwin, et al. (2005) J. Biol. Chem., 280. 21847-21853.Briefly, this colorimetric assay monitors the reduction of 2,6-dichloroindophenol (DCIP) at 600 nm (e = 18.8 mM-1cm-1) for measuring DHOD inhibition. The assay was carried out using a solution containing 100 mM HEPES, pH 8.0, 150 mM NaCl, 10% glycerol, 0.1% Triton X-100, 20 micro molar CoQD (coenzyme QD), 200 micro molar L-dihydroorotate, and 120 micro molar DCIP. Reactions are initiated by addition of enzyme to a final concentration in the range of about 5 nM to about 50 nM while maintaining the temperature of a circulating water bath at 25° C. Alternatively, for potent compounds, activity was determined by directly measuring the production of orotic acid at 296 nm (ε = 4.3 mM-1 cm-1).