The diurnal cycle in the heat budget of the upper equatorial Pacific Ocean is studied using 26 days of special high-resolution oceanographic and meteorological observations. The focus is on the turbulent heat fluxes at the base of the mixed layer, which are calculated as a residual in the mean diurnal heat budget. The inferred downward heat flux at the base of the mixed layer is 150 W m - 2 , averaged over the mean diurnal cycle, and ranged from near zero in the morning and early afternoon to 200 W m - 2 during the late afternoon until dawn. The inferred residual turbulent fluxes were used also to estimate the mean diurnal cycles in vertical eddy diffusivity and turbulent dissipation rate.