Tests of a formula derived for the cutoff wave number of vertical temperature gradient spectra, using data taken in the upper layers of the North Pacific, show encouraging results. To derive this formula, the cutoff wave number is assumed to be the Batchelor wave number, with kinetic energy dissipation calculated by combining a form used in the atmosphere for caLculating the vertical eddy diffusivity in terms of the dissipation with the Osborn-Cox formula for calculating eddy diffusivity from the variance of the temperature gradient spectrum. Kinetic energy dissipation in the water column can be determined in this way; a vertical profile of dissipation shows, values of the order of 10-3 cm2 s-3 at the base of a storm-tossed mixing layer. In the thermocline below, dissipation occurs in patches.