assigning variables to their defaults

Hi,

Is there any way to assign defaults values to the shell variables without reassigning them ( restarting the session)

for example
after login the value of ORACLE_HOME=/a/b/c
i have changed this value from the console
export ORACLE_HOME=/c/d

now what if i want the value exported to /a/b/c again..

Thanks in advane.

reload/source the environment that started it in the first place

> . $HOME/.profile