Heat transfer experiments are described that were conducted with hydrogen and helium gas flowing turbulentiy in smooth, round, electrically heated tubes. Values of the ratio of wall-to-fluid temperature from 1.6 to 11.1 were achieved by lowering the inlet temperature of the gas in a liquid nitrogen intercooler. Bulk Reynolds numbers ranging from 4,000 to 1,500,000 and inlet temperatures of the gas as low as 135 deg R (-325 deg F) were obtained in the experiments. Measurements were made of the pressure drop along the length of the test section in adiabatic and in diabatic flow. The results are presented in tabular and in graphical form. Correlation of the results was achieved by including the term (T/sub w//T/sub b/)/sup a/ in the Nusselt equation. Values of the correlation exponent, a, are presented for the reference temperatures employed for evaluating the transport properties of the gas. The presence of acoustic resonance in the flow was found to increase the heat transfer coefficient by as much as a factor of two. (auth)