Current understanding of the evolutionary history of young, high-z
galaxies is severely limited by lack of data on their dust content, and
its effects in absorption and emission.  The powerful long-wavelength
capabilities of ISOCAM make it possible for the first time to measure
directly dust in the brightest known normal star-forming galaxies at
z>2.  These objects are newly discovered, and were unknown before
ISO's launch.  We will combine accurate ground-based L-band
measurements of the stellar flux with 6, 12 and 15 micron ISOCAM
images to calculate the thermal emission from dust (the "infrared
excess") and determine accurately the fraction of stellar light
absorbed.  By measuring the re-emitted thermal spectrum, we will
compare the temperature distribution of dust with what is observed in
starburst galaxies at the current epoch.  These observations will also
be applicable to other cosmological problems, such as measuring the
Cosmic IR Background.