  Seyfert galaxies come in two main types (types 1 and 2) and the difference is
probably due to obscuration of the nucleus by a torus of dense molecular
material. The inner edge of the torus is expected to be ionized by optical and
ultraviolet emission from the active nucleus, and will radiate direct thermal
emission (e.g. NGC 1068) and will cause free-free absorption of nuclear radio
components viewed through the torus (e.g. Mrk 231, Mrk 348, NGC 2639). However,
the nuclear radio sources in Seyfert galaxies are weak compared to radio
galaxies and quasars, demanding high sensitivity to study these effects. We
have been making sensitive phase referenced VLBI observations at wavelengths
between 21 and 2 cm where the free-free turnover is expected, looking for
parsec-scale absorption and emission. We find that free-free absorption is
common (e.g. in Mrk 348, Mrk 231, NGC 2639, NGC 1068) although compact jets are
still visible, and the inferred density of the absorber agrees with the
absorption columns inferred from X-ray spectra (Mrk 231, Mrk 348, NGC 2639). We
find one-sided parsec-scale jets in Mrk 348 and Mrk 231, and we measure low jet
speeds (typically <= 0.1 c). The one-sidedness probably is not due to Doppler
boosting, but rather is probably free-free absorption. Plasma density required
to produce the absorption is N_e >= 2 x 10^5 cm^-3 assuming a path length of
0.1 pc, typical of that expected at the inner edge of the obscuring torus.
