Lumbricus terrestris, Allolobophora caliglnosa, and Eisenia foetida are vectors in the transmission of Heterakis gallinarum and Histomonas to chickens and turkeys. The infective stage for Heterakis was found to be the second-stage (first post-hatching stage) larvae. Earthworms from infected premises that were maintained 2 to 3 days in each of 3 or more changes of clean soil or 7 days on moist filter paper transmitted as many cecal worms and produced as many Histomonas infections as did worms of the same species and source fed directly from the contaminated soil. The worms'' castings produced no infections. Subjecting earthworms to either 1% formalin or 1.5% nitric acid prevented the transmission of Heterakis and Histomonas. Heterakis eggs were never found in dissected earthworms or in washings of parts of earthworms. Living larvae emerged from the tissues into the coelomic cavities of dissected worms, and into the medium i which intact worms were immersed.