Measurements of the isotopic compositions of sixty lead samples were made during 1963-1965 at the Chemistry Department of Brookhaven National Laboratory using a thermal-emission mass spectrometer as a help in tracing possible locations of the mines from which the leads could have been taken. The isotopic compositions of the archaeological objects do vary over a considerable range, but many fall into one of three definite groups. The same groups also include galena (lead sulfide) ores from 3 of the best-known ancient leadmining areas, Laurion, Southern Spain and Roman Britain. Isotope compositions of leads from widely separated sources may be indistinguishable if the deposits are geologically similar. Thus, isotope evidence alone cannot prove conclusively that lead from some given object was taken from some given area. The isotopic compositions of several objects made of lead known to have come from specific mining areas were found to match those of ores from the same areas.