The present invention provides methods and compositions for the detection and quantification of Cripto-1. In particular, the present invention provides methods and compositions for the detection and quantification of Cripto-1 in samples such as milk, plasma, serum, and other biological fluids. In particularly preferred embodiments, the present invention finds use in the detection and/or quantification of Cripto-1 in human milk, plasma, serum, and other biological fluids.