By exposure of adult hamsters as virus sentinels in southeastern México, Venezuelan encephalitis (VE) virus was found in several lowland regions along the Gulf coast of southeastern Veracruz state. Near the cities of Minatitlan and Coatzacoalcos and thence to the Tabasco border at the Rio Tonala, the virus was widely distributed throughout the relatively homogeneous brushy and wooded rural habitats. However, virus could be focal, as near Sontecomapan, where prevalences varied widely with type of habitat within a radius of 1.6 to 8 kilometers. Detectable virus activity diminished with height over 1.8 meters above ground at Sontecomapan and Minatitlan, and with altitude above sea level near Sontecomapan; it disappeared without apparent reason immediately south of Minatitlan and across the Isthmus of Tehuantepec. In the endemic areas of Veracruz, VE virus was detected yearly during 1963–67; .24 to .39 of exposed hamsters yielded VE virus after usually only 3 to 10 days of exposure, and isolations per 100 hamster-days exposure averaged from 2.4 to 4.0 (range 0 to 11.5). Surviving hamsters had no VE virus antibody, indicating that inapparent infection did not occur. At Sontecomapan, virus prevalences were similar during dry (February–May) and wet (July–September) months, but at Minatitlan and toward Tabasco, they were lower during the dry months. Sentinel suckling mice detected VE virus at Sontecomapan only during 1963, and were not as effective or practical to use as hamsters.