During the wet seasons of 1972 and possibly 1971, sentinel horses became infected by Venezuelan encephalitis (VE) virus in a temporally and geographically progressive manner inland from an enzootic marsh focus of virus on the Pacific coast of southeastern Guatemala. During the wet seasons of 1972 and 1973, VE virus was detected by sentinel horses (and a sentinel hamster in 1972) in a small woods 10 km north of the marsh, but virus was undetectable there during the dry seasons of 1973 and 1974 and the wet season of 1974. Culex (Melanoconion) mosquitoes were found in this woods and at the marsh during August 1973. These observations are compatible with movement of VE virus from the marsh habitat during some wet seasons. However, virus activity in this region adjacent to the marsh was quantitatively unpredictable on a yearly basis and occurred in only very focal habitats during 1971 to 1974. Mechanisms of VE virus movement from the marsh are currently unknown, but bats are under study as a likely possibility.