1. The hot strength of the Cr-Mo-V steel under investigation depends greatly on the heat treatment conditions. For the available composition the optimum treatment was normalizing at 1030–1050°C (1885–1920°F) and tempering for not less than 5 hours at 700–720°C (1290–1320°F). 2. The creep strength for this steel, after normalizing and tempering at 570°C (1060°F) is 6 kg/sq. mm (8500 psi) at a creep rate of 10−5%/hour. 3. The rupture strengths of the steel determined by extrapolation after the optimum heat treatment are 10. 5 kg/sq. mm (14,900 psi) at 570°C, 9. 3 kg/sq. mm (13,200 psi) at 585°C, and 7. 5 kg/sq. mm (10, 700 psi) at 600°C (1110°F). 4. The structure and room temperature properties of the steel after the recommended heat treatment did not suffer substantial change during rupture testing. 5. In its high temperature properties, this steel satisfies the requirements for use in power station equipment, operating on steam at 565–585°C (1050–1085°F) and 140 atm (2000 psi).