Palaeolimnological investigations in the volcanic highlands of central Mexico (19°N) have yielded clear evidence of environmental degradation associated with episodes of forest clearance and agricultural expansion during the last 3500 years. Preliminary results are presented from five lake basins situated at altitudes of 1700 to 2575 m above sea level, along a gradient of decreasing aridity and temperature from north to south: Hoya San Nicolás de Parangueo (Guanajuato); La Piscina de Yuriria (Guanajuato); Pátzcuaro (Michoacán); Zacapu (Michoacán); and Upper Lerma (Estado de México). Samples from sediment cores and pits are being analyzed for loss-on-ignition, magnetic susceptibility (chi and chi_fd), major cations, total phosphorus, carbon/nitrogen, carbonate content, delta¹³C, delta¹⁸O, diatoms, pollen, and charcoal content. Evidence for disturbance is provided by increases in nonarboreal pollen types, especially maize (<i>Zea mays</i>), peaks of chi, chi_fd and charcoal; increased concentrations of elements associated with soil material such as aluminum, iron, titanium, and phosphorus, and diatoms indicative of cultural eutrophication. Pátzcuaro, Hoya San Nicolás, Zacapu, and Upper Lerma show an initial phase of disturbance dating from ca. 3500 to 1400 BP, reflecting the widespread adoption of maize cultivation during the Preclassic. A later, more intense phase is recorded in all the basins. In Hoya San Nicolás, La Piscina de Yuriria, Zacapu, and Pátzcuaro, which lay within, or on the margins of the Tarascan state, this episode dates from Postclassic to Hispanic times (<1100 BP). In contrast, disturbance in the Matlatzincan area (the Upper Lerma Basin) was apparently more continuous, culminating during the late Classic to early Postclassic (ca. 1400-700 BP).