Local heat transfer coefficients were measured in a circular, copper tube of inner diameter 0.25 in., outer diameter 0.55 in., and length 36 in. Direct resistance heating of the tube wall from a direct current power source dictated the size and material of the test section. Since the electrical resistivity of copper varies appreciably with temperature, the radial heat flux was nonuniform along the length. (The temperature drop across the tube wall was small; therefore the heat flux in the radial direction was assumed uniform.) The test section was cooled from the inside with the eutectic alloy of sodium and potassium (22% Na, 78% K) flowing turbulently in a vertical direction. The range of variables covered in the experiment was as follows : fluid temperature from 85° to 1175°F, fluid velocity 4 to 60 ft/sec, Reynolds number 13,000 to 466,000, Peclet number 268 to 3850, average heat flux 28,600 to 3,200,000 Btu/(hr ft2). The maximum local heat flux was 6,000,000 Btu/(hr ft2). For the above test conditions the experimentally measured Nusselt numbers ranged from 1.4 at the low Peclet number to 22.4 at the high Peclet number. Most of the fully-developed Nusselt numbers found are lower than indicated by the Lyon-Martinelli equation, but are in quite good agreement with data of most other experimenters. The values of Nusselt number in the entrance region are about 40% higher than those predicted by Deissler, and approximately 10% higher than the data of Johnson, Hartnett, and Clabaugh. Near a Peclet number of 300, the Nusselt numbers observed were lower, by a factor of more than two, than the theoretical minimum for fully developed laminar flow. The reason for this abnormality has not been established.