The range and variety of environmental studies now in progress make it almost impossible to provide any all-encompassing statement of results. Almost all places associated with nuclear programs have become focal points of research in environmental biology. Fallout, deposited in patterns determined by the mechanisms of the atmosphere, has created at certain points on the earth’s surface—the Arctic, for example—ecological conditions that require investigation. New information of bioenvironmental significance has come in bits and fragments. We can, however, attempt to summarize what has been learned and to show, in broad terms, how radiobiological experience has extended appreciation of the earth as a single ecosystem—a system comprised of an infinity of interactions of water, land, and atmosphere, and of all living things. The spectrum of environmental investigation—investigations using man-made radioactivity—incorporates research in which: 1. Fallout radioactivity is assessed as a potential specific hazard to human populations. 2. Conditions created by fallout are examined for their potential long-term ecological significance. 3. Radionuclides introduced into the environment by nuclear tests, reactor operations, or other means are used as trace materials in basic studies in biological systems. 4. Radioactive forms of minerals and nutrients are deliberately introduced into biosystems—in measured amounts and under conditions of control—for studies of metabolic cycles and rates of flow of energy and nutrition. It will be useful to look in detail at some typical programs and results. ANIMAL RESEARCH [Illustration: _RAT. A lightly anesthetized, wild trapped rat is weighed and measured prior to marking it, taking a blood sample, and releasing it in a controlled ecosystem._] [Illustration: _FISH. Fisheries biologist with a large jackfish caught off Engebi Island, Eniwetok Atoll._] [Illustration: _COCONUT CRAB. Measuring the radioactivity of the shell of a coconut crab caught on Bikini Island._] [Illustration: _GEESE. Banding wild geese to study environmental effects of radionuclides on wildlife and possible entry of radionuclides into the human food chain._] [Illustration: _PLANKTON. An ingenious plankton trap is placed in a river as part of a long-range study of radionuclide uptake by aquatic organisms._] [Illustration: _SKATE. A clear-nosed skate being monitored by fisheries personnel to gather data on accumulation of radionuclides in its blood and tissues._] Wasps and Radioactive Mud At Oak Ridge National Laboratory, Tennessee, it was discovered in 1964 that two kinds of mud-dauber wasps were building their mud nests in equipment, cabinets, and electronic gear in the vicinity of a field station on the Oak Ridge reservation.