Cold—hardiness of stem sections of white ash (Fraxinus americana L.) from 10 geographic origins in eastern North America, growth in a provenance planting in south Michigan, was determined by controlled freezing. Northern plants were more cold—hardy than southern plants in early and midwinter, but differences disappeared by early spring. Substantial variation in cold—hardiness was found among trees within each origin. Multiple regression of killing temperatures on latitude, longitude, elevation, average annual minimum temperature, and annual frost—free period proved useful in predicting cold—hardiness, and may be useful in forecasting performance of trees in locations removed from their sites of origin.