The temperature difference ΔT across the cool skin of the ocean was determined from radiometric measurements of surface brightness temperature and conventional measurements of temperature at a depth of 1 m. Eleven days of measurements were made from the R/P flip in February 1974 about 800 miles north of Hawaii (35¿N, 155¿W). The surface brightness temperature was corrected for nonblackness of the surface to obtain an estimate of the true surface temperature. The constant λ in Saunders' (1967a) formula, ΔT = λ&ngr;Q/kU*, was found to be λ = 6.5¿0.6, where &ngr; is kinematic viscosity, Q the upward heat flux just below the interface, k the thermal conductivity, and U* the friction velocity. The constant is independent of wind speed for winds ranging from 3 to 11 m/s. The use of subsurface rather than surface temperature in the bulk aerodynamic formulas results in an increase in the sum of the sensible and latent heat fluxes equal to 4-5% of Q. However, the percentage change in sensible and latent heat fluxes may be much greater. Spectra of surface and subsurface sea temperature exhibit a peak at low frequencies and fall off approximately proportional to f-3/2 with increasing frequency f. The variability of sea surface temperature was caused about equally by the variability of subsurface temperature and the variability of ΔT. Caution should therefore be exercised in the interpretation of radiometric surface temperature measurement as a representive of subsurface temperature.