The effects of dynamo-generated magnetic fields in accretion discs are cons
idered for the two main types of diffusion mechanisms of turbulence and mag
netic buoyancy. Thin disc solutions are possible in both cases, and it is s
hown that the dynamo equations and vertical equilibrium place limits on the
turbulent parameters. A lower limit arises for the Prandtl number in the c
ase of turbulent diffusion.