Cercariae of F. hepatica axe shed by Stagnicola bulimoides techella generally during the winter and spring months in the Gulf Coast region of Texas, when standing water is present in the pastures. Unfavorable ecological conditions on Gulf Coast pastures created by the heat and drought of the summer destroy the cysts of the liver fluke early in the summer. Fluke-free sheep placed on 2 pastures Sept. 8, 1944, where resident fluke-infected sheep grazed, did not become infected until Dec. 1, 1944. Fluke-free sheep placed on an infested pasture July 3, 1945, did not become infected until Dec. 2, with the exception of one individual which acquired a light infection between Oct. 2 and Xov. 7. The period between the time when the cysts are destroyed in the summer and mass reinfestation of the pastures after the onset of the winter rains is sufficiently long to allow young flukes in the body to enter the bile ducts and develop to maturity. Immature migrating flukes are not destroyed by hexachlorethane or CCl4, the common fascioli-cidal drugs now in use. Treatment with hexachlorethane or CCI4 in the late fall when only adult parasites are present reduces the fluke population in the animals to the lowest possible number. Animals going into the winter season with light fluke infections spread fewer eggs, thus reducing the chances for large numbers of snails to become infected. The most important single time to treat animals for liver flukes in the Gulf Coast area is late in the fall before the onset of the winter rains. At least one more treatment in the early summer is recommended.