ABSTRACTWe have identified sultam thioureas as novel inhibitors of West Nile virus (WNV) replication. One such compound inhibited WNV, with a 50% effective concentration of 0.7 μM, and reduced reporter expression from cells that harbored a WNV-based replicon. Our results demonstrate that sultam thioureas can block a postentry, preassembly step of WNV replication.