We propose a program of high angular resolution imaging of the
 thermal emission from cool dust around a selection of pre-main-sequence
 young stars.   These observations will be used to constrain the
 contribution from extended envelope emission to the total thermal
 dust emission from the stars.  Work in our group and by collaborators
 using the Kuiper Airborne Observatory has shown that the far-infrared
 is a senstive region for detecting envelope emission.  We have also
 shown that many brighter pre-main-sequence stars have extensive
 envelopes which call into question the inference of circumstellar
 disks based solely on spectral energy distributions.  In this ISO
 proposal we plan to extend this research to fainter and lower
 luminosity sources, as well as to a broader range of stellar types.
 With these data we will have a much more complete picture of the
 relationship of envelope contribution to disk contribution over a
 range of stellar luminosity from a few solar luminosities to a few
 thousand solar luminosities.