Barrio Tepalcate, on the Los Perros River just outside Ciudad Ixtepec, Oaxaca, 18 km upriver from Laguna Zope, is one of the few Early and Middle Formative period sites known in the southern Isthmus of Tehuantepec region. Our salvage excavation in 2005 showed that the village covered no more than four hectares. It was probably one of several villages along the river in a two-tiered settlement hierarchy centered on Laguna Zope. The presence of Early Formative period ceramics suggests that the inhabitants of Barrio Tepalcate participated in the Early Olmec style horizon, although the design motifs on their pottery are simpler than those from San Lorenzo 150 km to the north. We found little evidence of imported ceramics from San Lorenzo, which may be due to the small size of the sample and the site, or to differences in how San Lorenzo interacted with highland sites, such as Etlatongo and San José Mogote, and Isthmian sites, such as Barrio Tepalcate. The Early Formative inhabitants of the southern Isthmus were members of the Mixe-Zoque language family, and specifically Mixe speakers by the Late Formative.