This is the fifth of a series of progress reports to the Environmental Health Surveillance Center of the University of Missouri; each report covers a six-month period in our reconnaissance geochemical survey of the State of Missouri that is designed to provide epidemiologists of the Environmental Health Center with data on the variability in the geochemical environment throughout the State. The survey is being directed at geologic units (including both surficial and bedrock units), both agricultural and uncultivated soils, native vegetation and farm crops, and both ground and surface waters. Emphasis is on the environment in its natural state; artificial pollution of the environment is being investigated in a few small areas-principally where such pollution is thought to complicate our efforts to determine the natural environmental character. Adequate knowledge of the natural environmental character is necessary in order to establish a background for judging the degree and extent of environmental pollution.