Captured bats were placed in cloth bags until processed. possibly a virus more closely related to dengue virus than to other flaviviruses. Each serum sample was assayed for flavivirus RNA by reverse transcription PCR, but all were negative. Keywords:Bats, Chiroptera, dengue virus, flavivirus, Mexico, surveillance Bats are one of the most abundant and geographically widespread groups of vertebrates. There are 1,116 recognized species of bats and they inhabit every continent (except Antarctica) and almost every ecosystem (Wilson and Reeder, 2005;Calisher et al., 2006). Bats are often found in areas inhabited by humans and harbor a diverse range of viruses of medical importance, including filoviruses, SARS-like and other coronaviruses, henipaviruses, and lyssaviruses. Dengue virus (DENV), West Nile virus (WNV), and St. Louis Imiquimod (Aldara) encephalitis virus (SLEV) are recognized human pathogens in the genusFlavivirus, familyFlaviviridae. The role of bats in the transmission and ecology of DENV, WNV, and SLEV is not well understood, but several studies have demonstrated that bats of some species are susceptible to infection by these viruses (Sulkin et al., 1966;Paul et al., 1970;de Thoisy et al., 2009). Dengue virus exists as four serotypes (DENV-1 to DENV-4), and all are present in the Yucatan Peninsula of Mexico (Lorono-Pino et al., Imiquimod (Aldara) 2004). Serologic data indicate that WNV and SLEV also occur in this region (Farfan-Ale et al., 2006). Nevertheless, there is no information on the infection or prevalence of antibody to these viruses or any other flaviviruses in bats in the Yucatan Peninsula. Dengue virusspecific nucleic acid and antibodies were detected in bats in the nearby states of Veracruz, and DENV-specific antibodies were detected in bats in the states of Colima and Jalisco in southwest Mexico (Aguilar-Setien et al., 2008). No other investigators have examined whether flaviviruses infect bats in Mexico. Our goal was to determine the occurrence of selected flaviviruses in bats in Merida, the largest city in the Yucatan Peninsula. We collected whole blood from 140 free-ranging bats captured using mist nets at five study sites, JulyOctober 2010. One site was within the central business district (CBD); the other four were directly to the north, south, east, or west of the CBD. The site within the CBD was in the Parque Zoologico El Centenario (Merida zoo; 20587.6N, 893826.0W). The northern site (Santa MGC5370 Gertrudis Copo; 210234.9N, 8935930.1W) was on a private property containing a sheep pen, an enclosure of chickens, low scrub, and sparse trees. The southern site (Parque Metropolitano; 205350.8N, 893931.10W) was established in a public park with abundant trees and other vegetation and three small caves. The eastern site (Acuaparque; 2056950.8N, 893440.4W) was in a public park containing Imiquimod (Aldara) a manmade lake, recreational facilities, low scrub, and native grasses. The western site (Parque Hundido; 2058936.8N, 893928.5W) was a public park with numerous trees, native grasses, and several ponds. We trapped four nights a week (one site per night) using three mist nets (62 m with 16-mm mesh openings) at each site. Nets were placed over water, along fruiting trees, and at the entrances of caves whenever possible. Nets were set from dusk (~7:00pm) until 11:00pm. Captured bats were placed in cloth bags Imiquimod (Aldara) until processed. Bats were identified to species, age class (juvenile or adult), and sex (Medelln et al., 1997). Taxonomy followedWilson and Reeder (2005). Approximately 100 L of blood was collected from each bat by nonlethal cardiac puncture or from the ulnar vein. Blood samples were diluted 10-fold using phosphate-buffered saline containing 0.75% bovine albumin fraction V, 500 units/mL penicillin, 500 g/mL streptomycin, and 12.5 g/mL amphotericin, and placed on ice. Samples were transported to the laboratory, centrifuged, and stored at 70 C. Sera Imiquimod (Aldara) were assayed by plaque reduction neutralization test (PRNT) following.