The dual-use dilemma in biological science is an emerging issue in biodefense. The possibility that new biotechnologies and research findings could be misused adds to concerns about "traditional" biological weapons such as anthrax, tularemia and other pathogens. In the past, the only option for developing biological weapons was to select strains for certain qualities including environmental stability, lethality, ability to be aerosolized, and antibiotic resistance. Now, with recombinant DNA technology and increased understanding of biological systems, desired characteristics can be engineered into pathogens and medical technologies applied to increase delivery of agents. Progress in biology and genetic manipulation will continue, and it is necessary to consider the existing biosecurity control measures and continue expand them to keep pace with technology development.