These experiments were undertaken to investigate the transfer of heat from solid surfaces to flowing water. The bulk temperature of the cooling water was below the boiling point, and the surface temperature of the heat transfer tube went to about 100 °C. above the boiling point. Water velocities ranged up to 10 ft. sec.−1and heat fluxes up to 720 w. cm.−2. The non-dimensionless heat transfer constantain the Dittus and Boelter formula (Nu) = a(Re)0.8(Pr)0.4, which under normal forced convection has a value of 2.30 × 10−2, increased to four times the normal value under the surface boiling conditions. It is shown graphically that the constantabears a simple relation to the heat flux and the length–diameter ratio for surface temperatures below a certain value. For constant heat flux and volume flow rate, the surface temperature rises with rising bulk liquid temperature until it reaches the certain value of the surface temperature referred to above. The surface temperature then remains constant with further rise in the bulk liquid temperature until conditions become too unstable for measurements.