A survey of gastro-intestinal parasites in cattle and sheep in Utah Valley was conducted. Cattle in the valley were not seriously parasitized by helminths, whereas sheep usually had heavy helminth infections. Ten genera of helminths and 8 species of coccidia were identified in cattle in the valley, and 14 genera of helminths and 8 species of coccidia were identified in sheep. In conjunction with the survey, meteorologic studies were conducted May through September, 1909, to ascertain the effects which irrigation had upon micro-environments on grass pastures in relation to the development of free-Iiving stages of gastro-intestinal nematodes of ruminants. The effects of irrigation were such that soil moisture remained high throughout the pasture season, and moisture released from the soil to the atmosphere was redeposited as dew almost every night during the study period. Temperature and moisture conditions were conducive for development and survival of gastro-intestinal nematodes during the entire 1969 pasture season.