  We prove a formula for the Fekete-Leja transfinite diameter of the pullback
of a set E in C^N by a regular polynomial map F, expressing it in terms of the
resultant of the leading part of F and the transfinite diameter of E. We also
establish the nonarchimedean analogue of this formula. A key step in the proof
is a formula for the transfinite diameter of the filled Julia set of F.
