Can't Remove Item List

I am attempting to remove an item list. I understand the item field associated to this list must be deleted first. When I try to delete the item field I recieve the following eror:

This custom field cannot be deleted because it is referred to by other custom fields.

This list and item field were created using the Matrix item assistant as a new list. How can the item field be related to another item field ? How can I determine what other item fields are referring to the one I just created ?

Thanks in advance.

Kyle