You need to manipulate the toolbar.items array.
Here is some code I use to hide and display a Done button. If your button is on the extreme edge of the toolbar or in-between other buttons your other buttons will move, so if you want your button to just disappear then place your button as the last button towards the centre. I animate the button move for effect, I quite like it.
-(void)initLibraryToolbar {
libraryToolbarDocumentManagementEnabled = [NSMutableArray arrayWithCapacity:self.libraryToolbar.items.count];
libraryToolbarDocumentManagementDisabled = [NSMutableArray arrayWithCapacity:self.libraryToolbar.items.count];
[libraryToolbarDocumentManagementEnabled addObjectsFromArray:self.libraryToolbar.items];
[libraryToolbarDocumentManagementDisabled addObjectsFromArray:self.libraryToolbar.items];
trashCan = [libraryToolbarDocumentManagementDisabled objectAtIndex:3];
mail = [libraryToolbarDocumentManagementDisabled objectAtIndex:5];
[libraryToolbarDocumentManagementDisabled removeObjectAtIndex:1];
trashCan.enabled = NO;
mail.enabled = NO;
[self.libraryToolbar setItems:libraryToolbarDocumentManagementDisabled animated:NO];
}
so now can use the following code to show your button
[self.libraryToolbar setItems:libraryToolbarDocumentManagementEnabled animated:YES];
trashCan.enabled = YES;
mail.enabled = YES;
or to hide your button
[self.libraryToolbar setItems:libraryToolbarDocumentManagementDisabled animated:YES];
trashCan.enabled = NO;
mail.enabled = NO;