Results of several recent reports on the role of ocean mixing in the transient response to a CO2 doubling are analyzed and compared. Wigley and Schlesinger (1985) obtained an analytical solution to a one-dimensional box-diffusion (BD) ocean model in which the mixed layer e-folding time &tgr;e∝f0 2KΔTeg 2, where f0 is the planetary ocean fraction. K is the ocean diffusivity, and ΔTeq is the equilibrium temperature response. The dependence of &tgr;e obtained by Wigley and Schlesinger is compared with that obtained using simple land-sea resolved and box-advection-diffusion (BAD) models. For a BAD model the dependence of &tgr;e on both K and ΔTeq is significantly less than for a BD model. A comparison of the transient response of BD and BAD models using the same effective K indicates that the behavior of the BAD model cannot be captured using a BD model, except during the first few decades of the transient response. Schlesinger et al.(1985) estimated atmospheric and mixed layer values of &tgr;e for their coupled atmosphere-ocean general circulation model (A/O GCM) by fitting a BD model to the first 16 years of their A/O GCM transient response and then integrating the BD model for 200 years. However, Schlesinger et al. appear to have overestimated values of &tgr;e for their long-term A/O GCM by fitting their short-term A/O GCM transient response to a model in which the equilibrium globally averaged atmospheric and mixed layer temperature responses are equal, whereas this is apparently not true for their A/O GCM. Hansen et al. (1984) estimated &tgr;e by modeling three-dimensional ocean mixing as a series of isolated BD models, one below each horizontal grid point, and by using tritium-based diffusion coefficients, which probably are too large when applied to heat and probably lead toan overestimate of the actual &tgr;e.