Principles of the thorium-230 dating method were applied to the study of thorium and uranium isotopes in a series of rain samples collected at Fayetteville (36°N, 94°W), Arkansas, since 1980. The results indicate that the rainwater contains volcanic ash materials with a wide variety of ages, which were blown up onto the upper stratosphere from the 18 May 1980 eruption of Mount St. Helens and the 28 March 1982 eruption of E1 Chichón. These volcanic materials seem to have stayed airborne for a number of years and profoundly affected the global atmospheric inventories of thorium and uranium isotopes.