Habitat fragmentation and diseases have resulted in a decline of the marsh deer (Blastocerus dichotomus) throughout its South American range. Our objectives were to determine whether marsh deer intended for translocation from a region of the Rio Paraná Basin had been infected previously by foot-and-mouth disease virus (FMDV) and whether they were carrying virus. We captured marsh deer from June to October 1998 and collected blood from 108 animals and esophageal-pharyngeal fluid from 53. Serum was tested for antibodies against three FMDV serotypes (O, A, and C) by liquid-phase-blocking sandwich enzyme-linked immunosorbent assay (ELISA). Esophageal-pharyngeal fluid was tested for FMDV RNA by reverse transcription polymerase chain reaction (RT-PCR) and inoculation into three successive baby hamster kidney (BHK-21) cell subcultures, followed by RT-PCR of cultures. We detected low log₁₀ titers (range 1.0–1.5) to FMDV subtype A₂₄ Cruzeiro in 19 of 108 sampled marsh deer, but failed to isolate FMDV or detect FMDV RNA in any samples. We conclude that marsh deer from our study site were unlikely to carry FMDV; however, as a preventive measure, the 19 animals with titers for FMDV were not sent to FMDV-free Brazilian states.