  Resistivity measurements are reported for single crystals of
Mn$_{12}$-Acetate and Fe$_8$Br$_8$. Both materials exhibit a
semiconductor-like, thermally activated behavior over the 200-300 K range. The
activation energy, $E_a$, obtained for Mn$_{12}$-Acetate was 0.37 $\pm$ 0.05
eV, which is to be contrasted with the value of 0.55 eV deduced from the
earlier reported absorption edge measurements and the range of 0.3-1 eV from
intramolecular density of states calculations, assuming $2E_a$= $E_g$, the
optical band gap. For Fe$_8$Br$_8$, $E_a$ was measured as 0.73 $\pm$ 0.1 eV,
and is discussed in light of the available approximate band structure
calculations. Some plausible pathways are indicated based on the crystal
structures of both lattices. For Mn$_{12}$-Acetate, we also measured
photoconductivity in the visible range; the conductivity increased by a factor
of about eight on increasing the photon energy from 632.8 nm (red) to 488 nm
(blue). X-ray irradiation increased the resistivity, but $E_a$ was insensitive
to exposure.
