The plant hormone abscisic acid (ABA) is a major growth regulator mediating several aspects of plant development and stress-induced processes. For the hormone to function within the cell, it must first interact with a proteinaceous receptor to commence transmission of a signal to downstream components that elicit a cellular response. With the identification of several ABA receptors, there is an increased interest in receptor–ABA interaction studies and a demand for easy-to-follow protocols to allow measurement and quantification of ABA binding. Here, we present protocols for radioligand-binding measurements with particular focus on the ABA-binding of the recently identified ABA receptors, ABAP1 and FCA.