We report 35 new and 9 revised terrestrial heat flow measurements overlying the Andean subduction zone in Bolivia and Peru. The measurement sites are distributed in the Andean Cordillera, the Altiplano, the sub-Andean ranges, and the sedimentary platform and basins to the east of the Andes. They fall in the distance range 75--900 km form the Peru-Chile trench. Sites in the Peruvian Cordillera have a mean heat flow of 41 mW m-2, whereas those in the Bolivian Cordillera and Altiplano average 84 mW m-2. The sub-Andean ranges and the adjacent sedimentary platform have a mean heat flow of 50 mW m-2. The higher heat flow of the Bolivian Cordillera and Altiplano lies to the east of Quaternary volcanoes along the Bolivia-Chile border and in southernmost Peru and thus can be recognized as a ''back arc'' heat flow high. Neither Quaternary volcanism nor high heat flow are present in central and northern Peru. This contrasting along-strike pattern correlates with the variable angle of subduction of the Nazca plate beneath the region. Beneath Bolivia the subduction is at about 30¿--35¿, whereas beneath Peru it is subhorizontal and may be providing a cold underplate to the overlying Peruvian lithosphere. Extensive Miocene volcanism in Peru suggests, however, that heat flow in Peru 10 Ma ago was likely similar to that in Bolivia in the present day and implies a chage in subduction and a rapid diminution of heat flow in Peru over the past 10 Ma. Imbrication of cold oceanic lithosphere beneath Peru, analogous to that beneath western British Columbia, may provide a mechanism for rapid reduction of the heat flow. ¿ American Geophysical Union 1988