With one conservative tracer in addition to salinity and potential temperature it is possible to determine the relative strengths of lateral and vertical mixing processes. This is achieved by first eliminating vertical advection through neutral surfaces and then forming a linear combination of the three conservative tracers so that the epineutral gradient (i.e., the lateral gradient along the neutral surface) of the new variable is zero, thereby eliminating lateral advection. The resulting expression for the ratio of the vertical and lateral diffusivities involves the curvatures of property-property diagrams formed both from vertical casts and from data measured on a neutral surface. The method requires that the epineutral gradients of potential temperature, salinity, and the third conservative tracer are parallel. This condition is often met in the common situation where water parcels are the result of mixing between just two parent water masses. ¿ American Geophysical Union 1991