One of emerging applications of SPR is measuring interactions between small molecules and G-protein coupled receptors (GPCRs). The SPR methods being developed in our laboratory are capable of measuring the direct kinetic characterization of GPCR interactions with their natural ligands or low molecular weight inhibitors. Compared to alternative technologies (radioligand assays, whole cell assays), SPR provides direct measurement of the interactions without introducing any non-specific interactions of ligands to proteins on cells. Once developed the assay is easy and time effective to perform. Kinetic information obtained is then important for further compound optimization for this important class of drug targets.