  There have been speculations about the need to find a new mechanism to
explain the colossal magnetoresistance exhibited by this material, having
pyrochlore structure and thus differing structurally and electronically from
the manganites. We will report here our transport results based on a two band
model, with conduction electrons and intermediate valence ions fluctuating
between two magnetic configurations. The model has been previously employed to
understand transport and thermodynamical properties of intermediate valence Tm
compounds and, in its periodic version, to analize the phase diagram. The
results obtained with this model for the transport properties of
Tl_{2}Mn_{2}O_{7} are in good qualitative agreement with the experimental
results.
