The crude protein and lysine digestibility values available in literature and ascertained in comparative investigations at the end of the small intestine (distal ileum) and in the complete digestive tract (faeces analysis method) of pigs were subjected to a correlation calculation in order to find out whether and to what degree there are relations between apparent 'ileal' and apparent 'faecal' digestibility. For both crude protein and lysine the relation between ileal and faecal digestibility is so close (r = 0.73 resp. 0.85 ... 0.98) so that for practical purposes it is not necessary to determine the apparent ileal digestibility for each feedstuff by means of the complicated cannula method. This can be calculated with great reliability from the experimentally ascertained apparent faecal digestibility. The differences between faecal and ileal digestibility are smaller for lysine (conversion factors 0.92 ... 0.99) than for crude protein (conversion factors 0.89 ... 0.93).