The results of an experimental investigation that examines the effects of one type of surface roughness upon heat transfer in a water-filled cubical enclosure are reported. The experiments covered the range from the beginning of transition to the point where the flow over 60 percent of the length of the heated side had undergone transition. Tests were conducted using both isothermal and constant flux boundary conditions. The largest increase in overall Nusselt number was 15 percent at Ra = 3.3 × 1010 on the isothermal heated plate. Increases of the local Nusselt number on the isothermal heated plate were as large as 40 percent. The roughness elements used in the present study were found to be ineffective on the upper portion of the heated plate where fluid detrains from the vertical boundary layer.