  The interaction between settling of dust grains and magnetorotational
instability (MRI) turbulence in protoplanetary disks is analyzed. We use a
reduced system of coupled ordinary differential equations to represent the
interaction between the diffusion of grains and the inhibition of the MRI. The
coupled equations are styled on a Landau equation for the turbulence and a
Fokker-Planck equation for the diffusion. The turbulence-grain interaction is
probably most relevant near the outer edge of the disk's quiescent, or "dead"
zone. Settling is most pronounced near the midplane, where a high dust
concentration can self-consistently suppress the MRI. Under certain conditions,
however, grains can reach high altitudes, a result of some observational
interest. Finally, we show that the equilibrium solutions are linearly stable.
