An experimental investigation of the effect of asymmetrical heating on fully developed turbulent heat transfer has been carried out. The test apparatus was a rectangular duel of aspect ratio 5:1. The duct was constructed so thai the two long sides of the rectangular cross section could be heated at different preselected rates, while the two short sides were unhealed. Two cases of asymmetrical healing were studied: (a) One of the two long sides was heated, while the second was unhealed; (b) both of the long sides were heated, with the heating rate at one side being twice that of the other. For the first case, the heat transfer coefficients are lower than those for the symmetrically heated duct. For the second case, the coefficients for the more strongly heated wall are also below the values for symmetrical heating, while the coefficients for the lesser-heated wall are greater than the symmetric heating results. These findings are in qualitative agreement with analytical predictions for the parallel-plate channel. Furthermore, by applying an analytically motivated correlation procedure (reference ),1 it was shown that overall Nusselt number results for asymmetric healing could be brought into virtual coincidence with those for symmetric healing.