The thermal development of a hydrodynamically developed turbulent flow in an isothermal-wailed circular tube has been investigated in complementary numerical and experimental studies. The numerical work was based on an algebraic turbulence model used in conjunction with the appropriate conservation laws. In the experiments the naphthalene sublimation technique was used to enable precise modeling of the boundary conditions. Comparisons of numerically and experimentally determined quasi-local Sherwood numbers were made throughout the entire thermal entrance region and into the fully developed region for Reynolds numbers between 5400 and S3, 500. The typical agreement between the numerical and experimental results was about three percent, with a maximum deviation of six percent. The predictions of the STAN5 computer code were found to be less accurate than those of the present numerical approach, as were the results predicted by a Graetz-type series solution.