The Report "RNA-Mediated Metal-Metal Bond Formation in the Synthesis of Hexagonal Palladium Nanoparticles" by Lina A. Gugliotti et al. published online in the 7 May 2004 issue of Science reported using a complex mix of RNA and water to create crystals of palladium. An ongoing investigation into this study by the U.S. National Science Foundation's (NSF) Office of Inspector General determined that the authors falsified research data. Although the NSF did not find that the authors' actions constituted misconduct, it nonetheless concluded that they "were a significant departure from research practices." Science is working with the authors to understand their response to the NSF final ruling. Depending on the outcome of this discussion, Science will issue either a Retraction or a (further) correction to the paper. In the meantime, Science is publishing this Editorial Expression of Concern to alert our readers that serious concerns have been raised about the validity of the findings in this Report.