SUMMARYStudies on three fungal hyperparasites onArceuthobiumspp. are reported.Wallrothiella arceuthobiiattacks only the spring-flowering Arceuthobia.Septogloeum gilliionA. campylopodumf.laricisandColletotrichum glocosporioidcsonA. campylopodumf.campylopodum, A. campylopodumf.laricis, andA. douglasiiare new host records.Pestalotia maculiformansis reported to occur onA. campylopodumf.abietinum.The potential of these fungi as biologic agents of control is discussed.