  The ISO coronal line spectrum of the brightest Seyfert galaxies from the CfA
sample is presented and modeled. ISO observations of [O IV] 25.9 $\mu$, [Ne V]
14.3 $\mu$, [Mg VIII] 3.02 $\mu$ and [Si IX] 2.58 $\mu$ lines are presented;
their relationship with the soft part of the ionizing spectrum from 50 to 300
eV is investigated. Pure photoionization models reproduce the line ratios,
setting ranges for the ionization parameter and the optical depth of the
emitting clouds. On the basis of the available data alone it is not possible to
distinguish between a power-law or a blackbody distribution as the intrinsic
shape of the UV ionizing spectrum. However, for the brightest Seyferts
analyzed, namely, NGC 1068, Circinus and NGC 4151, a black-body UV continuum is
favored.
