Abstract: Induction of RNA interference (RNAi) in human cells has enabled comprehensive functional annotation of the human genome via reverse genetic screens. Here we describe an optimized semiautomated method to produce, titrate, and screen large collections of short hairpin RNA (shRNA)-containing lentiviral vectors. We also present results from a pilot lentiviral RNAi screen for kinases whose silencing modulates sensitivity to a mitotic spindle protein kinesin-5 inhibitor (kinesin-5i). Our screen identified three distinct serine/threonine kinase 6 shRNA vectors within our library as enhancers of kinesin-5i-mediated HT29 cell growth inhibition. In contrast, three distinct shRNAs targeting cell division cycle 2/cyclin-dependent kinase 1 resulted in kinesin-5i resistance. These results demonstrate the feasibility of screening with large collections of lentiviral vectors to identify drug enhancers and suppressors.