The yeast two-hybrid system is a sensitive method to detect intracellular interactions between proteins. It has been successfully employed in the identification of novel interactors of several proteins, including adhesion molecules (for a general review on the method, see refs. 1 and 2). In general, the high sensitivity of the yeast two-hybrid system allows the detection of weak and transient interactions that escape biochemical analysis. Howewer, in some limited cases, interactions found with biochemical methods have not been reproduced in the yeast assay, possibly because of the lack of some posttranslational modifications. More generally, the high sensitivity of the yeast interaction assay may lead to the disclosure of false-positive protein-protein interactions. For this reason, it is always necessary to confirm the yeast interaction data using other methods of study for protein binding.