Preliminary investigations at Salar de Uyuni and the nearby salars (salt pans) of Coipasa and Empexa in the southern part of the Bolivian Altiplano show the presence of widespread lithium-rich brines. Widely scattered brine samples from Salar de Uyuni, which has an area of about 9000 km2 and is the largest salt pan on earth, show lithium values ranging from 80 to 1500 ppm. High values of 300-700 ppm are most prevalent in an area of about 2500 km2 in the east-central and southeastern part of the salar. A few brine samples in small areas in Coipasa and Empexa Salars have values ranging from 170 to 580 ppm Li. All the brines are essentially saturated with halite and are moderately high in sulfate (5000-15,000 ppm SO4) but low in carbonate (<500 ppm HCO3). Potassium and magnesium values are relatively high, chiefly in the range of 2000-20,000 ppm, and the K Mg ratio is about 1:1. The Li K and Li Mg ratios are relatively constant at about 1:20. The crystalline saline material and brines in these salars are residual from a former large lake, Lago Minchin, that occupied much of the southern Bolivian Altiplano during late Pleistocene time, augmented by saline material carried to the salars by streams since final drying of this lake. Thermal springs associated with rhyolitic volcanic rocks of Quaternary age may have been a major source of the lithium. ?? 1978.