Poly-ADP-ribose polymerases (PARPs) are enzymes that catalyze the post-translational transfer of adenosine diphosphate (ADP) from NAD+ to target proteins. Of the 17 PARPs, some have been studied extensively and are known to have important cellular functions while little is currenty understood about others. A cellular imbalance of one of these PARP enzymes, PARP4, has been correlated with several disease states, including cancers, though its cellular roles are largely unknown. Inhibitors of PARP4 are useful as tools to investigate the enzyme's functions and evaluate the inhibitors' therapuetic potential. In this research, several compounds were tested as inhibitors of PARP4 using a PARP inhibition screening assay. Initial results identified a potent, somewhat selective compound, and revealed which parts of the compound were important for PARP4 inhibition. This was used to direct the synthesis and testing of potentially more selective inhibitors of PARP4. This presentation discusses the inhibition results and their significance towards learning more about PARP4 biology, which can help inform researchers of this enzyme's role in disease states and give insight into developing treatments for such diseases.