It is known that some forage trees have potential defaunating capacity, as rumen protozoa population is reduced when ruminant are feed with them (Odenyo et al., 1997ª,b). The effect has been attributed to saponins (Diaz et al., 1992) and tannins (Odenyo et al., 1997a,b). It is also known that PEG binds to tannins and has been used to reduce the deleterious effect found in animals feed tanniferous trees (Makkar et al., 1998). However, to our knowledge it has not been studied if using PEG to increase digestibility will, on the other hand, affect the defaunating capacity of the tree. The objective of the present study was to develop a simple technique to screen forage trees for defaunation capacity and to assess if PEG could be used to overcome this effect.