Carnotite and possibly other radioactive minerals have been found recently in limestone in Ste. Genevieve County, Missouri. This is the first reported occurrence of carnotite, not only in Missouri but in the Mississippi Valley region. It is of interest scientifically because it is one of the few known occurrences of this mineral in limestone as contrasted with the more usual occurrences in sandstone typical of the Colorado Plateau region. From the practical standpoint this discovery opens new areas, both geologically and geographically, to the search for radioactive materials. The possibility of finding commercially valuable radioactive mineral deposits in areas and under conditions hitherto not considered favorable will stimulate prospecting and may result in the discovery of other new sources of uranium.