Regulators keeping tabs on possible new weapons of biological warfare need to monitor the synthesis of harmful DNA sequences of pathogenic organisms, a committee of scientists appointed by the National Research Council says. The concern arises from advances in synthetic biology that allow researchers to build custom genes for specially designed microbes. This ability has added new worries over possible chemical and biological warfare because individuals could create in the lab pathogens that were previously difficult to obtain. In a 187-page report released on Aug. 3, the NRC committee recommended modernizing the regulations covering research using the so-called select agents—82 potentially dangerous bacteria, viruses, and fungi—by defining the agents by their gene sequence and not by name alone. The change would allow regulators to monitor who is building or ordering parts of pathogenic agents. The report, which was requested by NIH, also concluded that developing a method of predicting harmful DNA sequences is scientifically unfeasible and that crafty individuals could build new toxic agents that do not occur naturally.