Cyclin-dependent kinase 5 (cdk5) is a member of the serine-threonine kinase family of cyclin-dependent kinases. This family is known for its role in the cell cycle, but cdk5 differs due to its interaction with activators p35 or p39, both abundant in post-mitotic neurons. Cdk5 is not known to have a role in cell cycle regulation at all, but is known to be an important modulator of neuronal activity. Cdk5 has been an attractive target for CNS diseases for a number of years. Among its attractions is the possibility that inhibitors will prevent the pathological phosphorylation of tau and neurofibrillary pathology in both Alzheimer's disease and tauopathies. More recently, there has been evidence that cdk5 is involved in the processing of pain and therefore inhibitors would also have potential therapeutic value for acute pain. Several classes of potent chemical inhibitors for cdk5 have been identified but most are competitive with the ATP binding site, resulting in a lack of specificity among the other cyclin-dependent kinases as well as other ATP-dependent kinases. We are working to discover specific inhibitors that might disrupt the interaction of tau and cdk5 at sites other than the ATP binding site. We are screening our compound library of 110,000 compounds using the full length tau as a substrate and will separate ATP competitive from non-competitive binders. In addition, we are taking a computational approach with virtual screening to identify non-ATP-competitive binders. These two approaches may lead to the discovery of site-specific inhibitors for tau and cdk5 interactions rather than competitive inhibitors for ATP binding. The hope is that non-ATP competitive compounds will more likely be selective and will be better therapeutics.