  We propose that the emission of the high excitation [OIV] line observed with
ISO in NGC 5253 and II Zw 40 is due to the presence of hot Wolf-Rayet (WR)
stars in these objects. We construct a consistent evolutionary synthesis and
photoionization model which successfully reproduces the constraints on their
massive star content and the relevant optical and IR emission lines including
[OIV] 25.9 micron. Our explanation for the origin of [OIV] is supported
empirically by: 1) the simultaneous presence of nebular HeII and [OIV] in these
objects, and 2) the close relation between nebular HeII and WR stars in
extragalactic HII regions. Photoionization by hot WR stars is mainly expected
to be of importance in young low metallicity galaxies. Alternate mechanisms are
likely at the origin of [OIV] emission in other objects.
