  We have studied the parsec-scale structure of the quasar 3C345 at
\lambda\lambda 1.3, 2, 3.6, and 6 cm, using total intensity and linear
polarization images from 3 epochs of VLBA observations made in 1995.84,
1996.41, and 1996.81. The images show an unresolved "core" and a radio jet
extending over distances up to 25 milliarcseconds. At 1.3 and 2 cm, images of
the linearly polarized emission reveal an alignment of the electric vector with
the extremely curved inner section of the jet. At 6 cm, the jet shows strong
fractional polarization (m~15%), with the electric vector being oriented
perpendicular to the jet. This is consistent with the existence of a transition
from the shock-dominated to the plasma interaction-dominated emission regimes
in the jet, occurring at a distance of ~1.5 milliarcseconds from the "core".
