  We investigate the influence of a uniform magnetic field on the zero-point
energy of charged fields of two types, namely, a massive charged scalar field
under Dirichlet boundary conditions and a massive fermion field under MIT
boundary conditions. For the first, exact results are obtained, in terms of
exponentially convergent functions, and for the second, the limits for small
and for large mass are analytically obtained too. Coincidence with previously
known, partial result serves as a check of the procedure. For the general case
in the second situation --a rather involved one-- a precise numerical analysis
is performed.
