A new procedure for analyzing lead and uranium ores which aids in the more precise determination of the age of the uranium ores has been developed in a joint research project at Argonne National Laboratory and the University of Chicago. Greatly increasing the sensitivity of the measurement of the four isotopes of lead in a given sample, the new technique has been successfully used in studying rocks containing as little as one part per million of uranium. Because it reveals more about the nature of the billion‐year‐old ores, the method may eventually contribute to more successful uranium exploration. The new means of analysis was developed by George Tilton and Clair Patterson, graduate students in the University of Chicago's Department of Chemistry. They worked under the guidance and with the assistance of Harrison Brown, associate professor of chemistry in the University's Institute for Nuclear Studies, Mark G. Inghram of the Institute and Argonne National Laboratory, and David C. Hess of the Laboratory's physics division.