xhost not working in new X11

I upgraded from X.4 to X.5 and the command xhost stopped working normally in the new X11. I'm not sure exactly what is wrong, but when I launch X11, any xhost command returns "xhost: Command not found." If I close the xterm window and choose "Applications -> Terminal" (or hit command-N) to open a new xterm window, the command works normally. What is it with the default xterm window that would prevent commands such as xterm from working normally?