The ejecta from SN 1987A is expected to strike the circumstellar
 nebula around the SN, ramping up to a bright source by about 1997.
 A flux of thermal photons up to approximately 100 eV is expected
 to be emitted, producing high ionization states (up to Fe XIV,
 for example).  A number of abundant elements (O, Ne, Mg, Al, Si, S)
 have strong forbidden lines due to high excitation states (VI to
 IX) and are expected to emit strongly in the wavelength range 3.0-
 34.9 micron.  This suite of lines will allow ionization state and
 and composition to be inferred.  Such SWS data would allow a check
 on less detailed compositional measurements attempted in the UV,
 and the IR lines are crucial to separating conditions in the ejecta
 and in the circumstellar nebula that existed before the explosion.
 A time-series of observations will allow a determination of the
 hardening of ionization as the collision between ejecta and nebula
 evolves.  We plan to observe from the ground the companions to many
 of these lines ([Si VI]1.960micron, [Al IX]2.040micron,
 [Si VII]2.478micron, [Fe X]6374A and [Fe XIV]5304A) to
 complement images at ISO resolution (2 to 7 arcsec) with < 1 arcsec
 FWHM ground-based images for the 5-arcsec wide nebula.  We will
 monitor this activity from the ground on a regular basis, and
 propose to obtain three epochs of data with ISO.  For a spring
 launch, this should be straightforward.  (Sky visibility would be
 nearly 100%.)  For autumn launch, it is about 20%, and will imply
 two observing epochs.