cdc42/Rac belongs to the superfamily of small GTPases that are structurally linked to the proto-oncogene product p21ras and are important for the control of cell growth and differentiation as well as for intracellular organization. Cdc42/Rac is an important upstream regulator of the protein kinase cascade that controls the SAPK/JNK and p38 activity. Recent data also sμggest that constitutive active forms of cdc42 can induce apoptosis throμgh a mechanism requiring signaling throμgh SAPK/JNK.