We propose observations of the heavy-element interior of supernova
 SN1987A utilizing the [NiI] (7.51 microns), [NiII] (6.64 microns),
 [FeI] (24.04, 34.71 and 51.29 microns), [FeII] (25.99, 35.34 and
 51.68 microns), and [FeIII] (22.93, 33.04 and 54.31 microns) lines.
 These measurements are a followon to our successful iron and nickel
 line studies from the Kuiper Airborne Observatory (Erickson etal.
 1988; Haas etal. 1990; Wooden etal. 1993; Colgan etal. 1994).
 Utilizing the increased sensitivity of ISO, we will continue to probe
 the evolution of the ionization states, densities, and temperatures
 of the iron-rich regions of the ejecta, and ascertain the existence
 of a central energy source (i.e. a pulsar).