It is now established that pre-main sequence stars are often
 surrounded by circumstellar disks, some of which are thought to be
 protoplanetary disks.  We propose to study the evolution of the dust
 in the disks by studying the CO and CO2 absorption bands in dust
 grains.  Since CO2 is produced by surface processing of CO, the
 abundance of CO2 with respect to CO is a direct measure of the
 amount of surface processing undergone by the grains.  Our spectra
 will cover the 4.27 micron band, by far the strongest fundamental
 band of CO2.  This band has been inobservable until now because
 it is located in a region completely inaccessible to ground-based
 telescopes and airborne platforms.  ISO provides the first
 opportunity to study CO2 in dust grains.  Our proposed research
 differs from the guaranteed time proposals in that our observations
 will provide the high resolution spectra necessary for modeling.