  We have examined theoretically the phenomenon of Electromagnetically Induced
Transparency (EIT) in a three-level system operating in the
lambda-configuration in presence of an externally injected noise coupling the
ground level to the intermediate (metastable) level. The changes in the depth
and the width of the induced transparency and the slowing down of the probe
light have been calculated as function of the probe detuning and the strength
of the injected noise. The calculations are within the rotating-wave
approximation (RWA). Our main results are the reduction and the broadening of
the EIT with increasing strength of the injected noise, and a reduction in the
slowing down of group velocity of the probe-laser beam. Thus, the injected
semi-classical noise, unlike the quantum-dynamical noise associated with the
spontaneous emission, is not effectively cancelled by the EIT mechanism.
