  We study the general form of the equations for isotropic single-scalar,
multi-scalar and dyonic $p$-branes in superstring theory and M-theory, and show
that they can be cast into the form of Liouville, Toda (or Toda-like)
equations. The general solutions describe non-extremal isotropic $p$-branes,
reducing to the previously-known extremal solutions in limiting cases. In the
non-extremal case, the dilatonic scalar fields are finite at the outer event
horizon.
