IGF (Insulin like Growth Factor) signaling is mediated by the ligands IGF1 and IGF2, and the receptors IGF-1R (Insulin like Growth Factor-1 Receptor), IGF-2R, and IR (Insulin Receptor). Additionally, downstream signaling from IGF-1R/IR through the PI3K signaling pathway is accomplished due to the adaptor protein IRS-1 (Insulin Receptor Substrate-1) binding to the phosphorylated and activated IGF-1R or IR. IR and IGF-1R signaling play a key role in normal development, growth, metabolism, and cellular homeostasis as well as being implicated in such disease processes as growth abnormalities, metabolic processes, and different types of cancer. Pharmacological disruption of IGF-1R/IR signaling is a fertile area of research, but due a critical role in normal cellular metabolism and growth, the ability to identify selective therapeutics targeting abnormally signaling cells would be greatly advantageous. This kit provides the assay-specific components for the quantitative determination of phospho-IGF-1R, phospho-IR, and phospho-IRS-1 in human whole cell lysates.