To help evaluate the applicability of variations of radon-222 in ground water and soil gas as a possible earthquake predictor, measurements were conducted in conjunction with underground explosions at the Nevada Test Site (NTS). Radon fluctuations in ground water have been observed during a sequence of aftershocks following the Oroville, California earthquake of 1 August 1975. The NTS measurements were designed to show if these fluctuations were in response to ground shaking; if not, they could be attributed to changes in earth strain prior to the aftershocks. Well waters were periodically sampled and soil-gas /sup 222/Rn monitored prior to and following seven underground explosions of varying strength and distance from sampling and detector locations. Soil-gas /sup 222/Rn contents were measured by the alpha-track method; well water /sup 222/Rn by gamma-ray spectrometry. There was no clearly identifiable correlation between well-water radon fluctuations and individual underground tests. One prominent variation in soil-gas radon corresponded to ground shaking from a pair of underground tests in alluvium; otherwise, there was no apparent correlation between radon emanation and other explosions. Markedly lower soil-gas radon contents following the tests were probably caused by consolidation of alluvium in response to ground shaking.