The behavior of the flux Richardson numberRf, as a function of the overall Richardson numberRi0, was investigated for a stably stratified, grid-generated, turbulent flow evolving in a closed-loop water channel. The turbulent dissipation rate ε, the buoyancy or vertical mass fluxpwbar; and the rms density fluctuation ρ′ were obtained from simultaneous single-point measurements of the horizontal and vertical velocity components and density fluctuations. From these,RfandRi0were calculated at each point in the spatially evolving flow. The resulting curves ofRfvs.Ri0exhibit the full range of behavior found in the very different case studied by Linden (1980). The length scale arguments of Gibson (1980) and Stillingeret al.(1983b) provide an underlying mechanism which successfully accounts for the shape of theRfvs.Ri0curve.