  We have carried out an extensive search for X-ray emission from young, very
low-mass objects near and beyond the substellar limit, making use of archived
ROSAT PSPC and HRI observations pointed at Brown Dwarfs and Brown Dwarf
candidates in the young sigma Orionis and Taurus-Auriga associations. In sigma
Ori we identify three Brown Dwarf candidates with X-ray sources; in
Taurus-Auriga we add one further X-ray detection of a Brown Dwarf to the list
published earlier. We combine this data with all previously X-ray detected
Brown Dwarfs and Brown Dwarf candidates in young stellar associations and star
forming regions to perform a study of stellar activity parameters on the as yet
largest sample of young, very low mass objects. A similar relation between
X-ray and bolometric luminosity, and H-alpha emission, respectively, as is
known for T Tauri stars seems to hold for young objects down to the substellar
limit, too. No signs for a change in X-ray activity are found on the transition
to substellar masses.
