The FGL1:LAG3 TR-FRET Assay is designed to measure the inhibition of LAG3 binding to FGL1 in a homogeneous 96 or 384 reaction format. This TR-FRET-based assay requires no time-consuming washing steps, making it especially suitable for high throughput screening applications. The assay procedure is straightforward and simple; a sample containing biotinylated LAG3, His-tagged FGL1 protein, and an inhibitor are incubated for one hour. Then, anti-His Tb donor and dye-labeled acceptor are added and fluorescence intensity is measured using a fluorescence reader.