A predaceous fungus, Acrostalagmus sp., was found attacking the larvae of Haemonchus contortus in cultures of sheep faeces. An attempt to propagate the fungus in maize meal and infect cultures of faeces was unsuccessful. Administration to sheep of material from faecal cultures containing the fungus gave inconclusive results. The possible use of fungi of this type, which attack their prey by penetration of the cuticle after spores have become adherent, as a means for biological control of nematode parasites is briefly discussed.