  We give an explicit expression for the entanglement of formation for
isotropic density matrices in arbitrary dimensions in terms of the convex hull
of a simple function. For two qutrit isotropic states we determine the convex
hull and we have strong evidence for its exact form for arbitrary dimension.
Unlike for two qubits, the entanglement of formation for two qutrits or more is
found to be a nonanalytic function of the maximally entangled fraction in the
regime where the density matrix is entangled.
