The eight-year record of mass balance of Peyto Glacier is correlated to meteorological data measured near the glacier and at Lake Louise 30 km to the south. The period investigated includes the highest and lowest accumulations for the past 40 years. The primary controls of net annual balance are seen to be the depth of the winter snow pack and the temperature record during the summer. Extensive summer snowfalls in the ablation area can slow down melt rates very considerably and affect the net annual balance positively. The variable nature of winter accumulation and its influence on snowline retreat and ice melt is illustrated by three years' data.