Mast cell degranulation is a critical step in the early phase of hyper-responsiveness in allergic diseases and Rho GTPase signaling has been established as a necessary step in degranulation.39 The Rho GTPases RhoA, Rac1, and Cdc42 have all been shown to have roles in mast cell degranulation through pharmacologic inhibition or genetic manipulation.5,31,37,40 Our goal was to determine how Rho GTPases are potentially regulated during FcεRI-mediated degranulation by examining their known regulators. Here, CDC42 is linked to allergic disease.