Resetting Environmental Variables

Hello, I often update the environmental variables (such as PATH, CLASSPATH, JAVA_HOME, TOMCAT_HOME, etc.) in my .profile when I install new software. But in order for the new values to take effect, I log out of my x session (gnome in my case), and then log back in. Is there any way for the new values of environmental variables to take effect without logging out and back in? Thanks very much. Dom