Pollen analysis from a sedimentary section in the valley of the Sauce Grande River (southwestern Buenos Aires Province) and a peat core from the Andorra Valley (southern Tierra del Fuego) provides evidence for the apparent large-scale synchroneity of major past vegetational changes and inferred climatic trends during the late Pleistocene and Holocene in this region. Climate before 10,000 years B.P. was relatively cold and dry, both in southwestern Buenos Aires Province and in southern Tierra del Fuego. A climatic amelioration to warmer and wetter conditions during the late Pleistocene and early Holocene is recorded in both regions. Late Holocene climates show greater variability and they suggest the onset of modern environmental conditions as represented by cool and wet conditions in southern Tierra del Fuego, and by arid to semi-arid conditions in southwestern Buenos Aires Province.