iframe calling parent javascript

Is it possible for me to setup an iframe so it calls a javascript function available in the window.parent.document scope?

If I am understanding the question correctly, assuming functionName() is defined within the parent of iframe, you can do this within your iframe:

window.parent.functionName();

This will only work though, if both parent and iframe are on the same domain: http://softwareas.com/cross-domain-communication-with-iframes