Transients in the heat content in Santa Monica and San Pedro Basins imply a basin-wide diapycnal eddy difusivity greater than 1 cm2/s. This is significantly larger than the value for SF6 of 0.25¿0.08 cm2/s determined for the interior of Santa Monica Basin for September 1985 to February 1986 by Ledwell and Watson (1991). Howver, the exodus of SF6 from Santa Basin after February 1986, by which time the tracer had mixed to the boundaries of the basin, was fast enough to be consistent with a greatly enhanced vertical flux. Since the kinetic energy in the basin had not changed significantly, it is unlikely that a temporal increase in forcing resulted in enhanced fluxes in the interior of the basin. The most likely interpretation is that diapycnal fluxes in the basin are dominated by processes in the boundary regions. Temperature and SF6 profiles from near the edges of the basin do not give conclusive evidence either for or against such enhanced mixing. ¿ American Geophysical Union 1995.