Secular equilibrium of the U series is usually assumed in measuring the dose rates from both the soil and the pottery matrix. This assumption was tested and found to be seriously in error in some cases. No single technique, such as alpha counting, can reveal this discrepancy. A combination of delayed fission neutron analysis, Ü3-ray spectrometry, and mass spectrometry were used to determine the magnitude of this disequilibrium and locate where it occurs in the decay chain. A disequilibrium ratio of 60% was found in come Jericho pottery. A significant effect on the thermoluminescent dating of pottery can be caused by this effect. -- AATA