The distribution, habit, and variation in Eucalyptus regnans F. Muell. are briefly described. It is shown that E. regnans almost certainly forms hybrids with E. obliqua. The seedlings of E. regnans are relatively frost-sensitive, and this sensitivity is increased by manuring with organic nitrogen. Under artificial frost, softened seedlings are killed at temperatures below 25–27°F, whilst well-hardened seedlings are killed at temperatures below 20–22°F. In the field the lethal frost temperature is some degrees lower. Ecoclines exist in the E. regnans populations in south-central Victoria. The seedlings show a gradation in both frost resistance and growth rate along altitudinal gradients. Seedlings derived from trees growing at the edge of a frost pocket at Wallaby Creek (2000 ft) combine a relatively high frost resistance (equal to that of seedlings at 3'700 ft) with a high growth rate.