Cyclin-dependent kinase 4 (CDK4) assembles with the "D" type of Cyclins, e.g. cyclins D1, D2, and D3, and play a pivotal role in the cell cycle entering the S phase. Dysregulation of the activity of CDK4 is related to many different cancers, indicating CDK4 inhibitors as promising anticancer treatments. In fact, multiple CDK4 inhibitors, including Palbociclib, were approved by the FDA recently. The CDK4 Assay Kit is designed to measure CDK4/CyclinD3 activity for screening and profiling applications, using Kinase-Glo® Max as a detection reagent.