Soil radon emanation increased sharply on the Rough Creek fault near the Illinois-Kenucky border in April 1980, 3 1/2 months before a M5.1 earthquakes in eastern Kentucky, July 27, 1980. The spikelike anomaly was similar to a radon anomaly in the New Madrid seismic zone in 1979 that preceded by 2 months a M3.9 tremor at the site of that anomaly. Weekly radon monitoring was initiated on the Rough Creek fault after abrupt cessation of spring flow on the fault occurred at a site that had experienced similar flow cessation 1 month prior to a M5.3 earthquake in southeastern Illinois in 1968. Although the recent Kentucky epicenter was 380 km east of the site of the detected radon anomaly, facors relating to regional structures, recent seismicity, additional radon data, and the stress regime suggest that the hydrologic and radon anomalies may have been precursors to an eastward progression of strain that culminated in the eastern Kentucky tremor.