Speculations regarding the mode of transmission of monocystid parasites of earthworms over a period of more than 100 years have never been tested experimentally under controlled conditions. In order to do so a stock of infection-free Eisenia foetida (Sav.) was raised from cocoons and experimental infections were induced in this host using sporocysts of the gregarine parasites Apolcystis elongata Phillips and Mackinnon 1946, and Nematocystis elmassiani (Hesse, 1909). Experimental infections were obtained by feeding to uninfected worms sporocysts obtained from infected host worms. This proved that the intervention of a vector is not a necessary condition of infection. Infections could not be induced by injecting sporocysts through the body wall into the body cavity. Infections are thus probably acquired in nature by the ingestion of sporocysts. Sporocysts do not leave the body of the host by being passed from coelom to lumen of the gut, nor do they pass directly to the exterior through apertures of the body wall. There was no evidence of parasitic autotomy. It is therefore concluded that death and decay of the host is the normal method of dissemination of sporocysts. Sporocysts were not infective after drying in air for three weeks. Other sporocysts lost potency after storage in moist conditions for several months. Infections involving the organisms specified were sporadic and unpredictable; modifying factors, such as variations in host suseptibility and latency in infection, appeared to be operating.