Setting a variable in the parent form

hey guys, i have a script which must send some info to the script which called it, basically i want to know how to send a varible to the parent page. i want to use this set variable in php.

currently i use this

parent.document.contactDetails.retaddress.value = 'something' ;

but this is just for a hidden form element, i want to set a variable in the parent form so i can use the value in the hidden form element as well as other places

is this possible?