The article reports on a research project (sponsored by EPA, EPRI, and Southern Company Services) to evaluate sodium conditioning as a possible solution to performance deficiency problems encountered at a number of major utility plants during the development of an unexpected, time-dependent degradation of performance of hot-side electrostatic precipitators (ESPs) collecting ash from certain coals (usually low-sodium low-sulfur coals). The article concludes that sodium conditioning produced by sodium sulfate addition to the coal supply is an effective way to improve the performance of a hot-side ESP which has undergone the sodium-depletion high-resistivity pattern of performance deterioration. Although the reported results are believed to be of general significance, certain characteristics of the operating parameters at Gulf Power Co.'s Lansing Smith plant are noteworthy with regard to the success of the conditioning process. First, ash concentration and composition, and boiler design, allowed the addition of the required amount of sodium without creating boiler operating problems. Secondly, the calcium content of the coal was moderate, and there is some evidence that high calcium concentrations would require more sodium addition for the same degree of resistivity reduction. Applicability of the process for other ash chemistries and operating conditions remains to be determined.