To initiate a discovery effort to identify potential scaffolds for selective inhibitors of human CYP2A13, a high throughput screening campaign was conducted. A cuvette-based assay based on UV/Vis absorbance changes upon ligand binding (described in Methods) was miniaturized and adapted for screening in 384-well format. Fig. 1 summarizes data from the high throughput screen. An average Z’ score of 0.89 ± 0.08 was obtained from positive (CYP2A13+PEITC) and negative control wells (CYP2A13+DMSO), which is an acceptable dynamic range for a high throughput screening assay. Primary screening of 35,200 Chembridge library compounds resulted in a high hit rate of 1.4%. This relatively high hit rate likely reflects the nature of the target. Xenobiotic-metabolizing cytochrome P450 enzymes have evolved to be promiscuous and would be expected to bind a higher number of library compounds than most proteins. Of the 508 primary screen actives that were repurchased and tested for binding with both CYP 2A13 and the 94% identical CYP2A6, 93 compounds were found to bind to CYP2A13 specifically (ΔAbs 385-419 nm > 0.2) compared with CYP2A6 (ΔAbs 385-419 nm