  We present ROSAT PSPC and HRI images of eight galaxies selected from a
distance-limited sample of 22 edge-on Seyfert galaxies. Kiloparsec-scale soft
X-ray nebulae extend along the galaxy minor axes in three galaxies (NGC 2992,
NGC 4388 and NGC 5506). The extended X-ray emission has 0.2-2.4 keV X-ray
luminosities of $0.4-3.5 \times 10^{40} erg s^{-1}$. The X-ray nebulae are
roughly co-spatial with the large-scale radio emission, suggesting that both
are produced by large-scale galactic outflows. Assuming pressure balance
between the radio and X-ray plasmas, the X-ray filling factor is $\gapprox
10^4$ times larger than the radio plasma filling factor, suggesting that
large-scale outflows in Seyfert galaxies are predominantly winds of thermal
X-ray emitting gas. We favor an interpretation in which large-scale outflows
originate as AGN-driven jets that entrain and heat gas on kpc scales as they
make their way out of the galaxy. AGN- and starburst-driven winds are also
possible explanations in cases where the winds are oriented along the rotation
axis of the galaxy disk.
