The increased difficulty and expense of using live animals for delivering infectious blood meals in arthropod-borne virus vector competence experiments has resulted in an increase in the use of artificial feeding systems. Compared to live hosts, artificial systems require higher viral titers to attain mosquito infection, thereby limiting the utility of such systems with low or moderate titer virus stocks. Based on the report that freshly propagated virus is more infectious than previously frozen virus, we determined whether such a preparation would enhance the ability to use artificial feeding systems. Culex quinquefasciatus and Aedes aegypti mosquitoes were offered blood in artificial membrane feeders containing freshly collected or previously frozen St. Louis encephalitis and dengue serotype-2 viruses (family Flaviviridae), respectively. Infection rates and estimates of vector competence were significantly lower (P < 0.05) for mosquitoes feeding on blood meals containing frozen-thawed compared to freshly collected virus. We indicate that the use of freshly propagated virus in artificial feeding systems can be an effective blood delivery method for low-titer viruses and viruses that are otherwise inefficient at infecting vectors in such systems. Fresh viruses used in artificial feeding systems may be a viable alternative to the heavily regulated and expensive use of live animals. © 2007 Elsevier B.V. All rights reserved.