Abstract Rap1 has been implicated in the regulation of morphogenesis and cell–cell contacts in vivo (Asha et al., 1999; Hariharan et al., 1991; Knox and Brown, 2002) and in vitro (Hogan et al., 2004; Price et al., 2004). Among cell–cell adhesion molecules regulated by Rap1 is cadherin, a calcium‐dependent adhesive receptor. Assembly of cadherin‐mediated cell–cell contacts triggers Rap1 activation, and Rap function is necessary for the stability of cadherins at junctions (Hogan et al., 2004; Price et al., 2004). Here we describe assays to access the effects of Rap1 on cadherin‐dependent adhesion in epithelia, in particular the method used for Rap1 localization, activation, and function modulation by microinjection. We focus on controls and culture conditions to determine the specificity of the phenotype with respect to cadherin receptors. This is important, because different receptors that accumulate at sites of cell–cell contacts are also able to activate Rap1 (Fukuyama et al., 2005; Mandell et al., 2005).