Hide the rightBarButtonItem of a navigation controller

Try

self.navigationItem.rightBarButtonItem = nil;

When you want it back though you will have to instanciate a button i.e.

UIBarButtonItem *rightBarButton = 
 [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemSearch
                                               target:self
                                               action:@selector(searchBar:)];
self.navigationItem.rightBarButtonItem = rightBarButton;
[rightBarButton release];