This research proposal aims at a better understanding of the
 physical properties of mass outflows from young stellar objects
 in different evolutionary stages. Using ISO's LWS
 we expect to gain new information concerning
 the nature of the driving source, the mass loss rate, the
 collimation, the excitation condition in the outflow region and
 the physical properties of the circumstellar mass distribution.
 Furthermore, with the new data we hope to discriminate among
 conflicting models by constraining their parameter spaces.
 We request 9 hours for line scans at medium and high resolution
 (autumn launch). For spring launch 8.2 hours are foreseen.