A multitracer study of a small aquifer in northern Switzerland indicates that the atmosphere in central Europe cooled by at Least 5 degrees C during the Last glacial period. The relation between oxygen isotope ratios (delta(18)O) and recharge temperatures reconstructed for this period is similar to the present-day one if a shift in the delta(18)O value of the oceans during the ice age is taken into account. This similarity suggests that the present-day delta(18)O-temperature relation can be used to reconstruct paleoclimate conditions in northern Switzerland. A gap in calculated groundwater age between about 17,000 and 25,000 years before the present indicates that during the Last glacial maximum, local groundwater recharge was prevented by overlying glaciers.