Actually the previous answer is correct only if you deal with ISIS-2 cubes. But, most people are now using ISIS-3. In this case, one of the simplest ways to import/read ISIS cubes into ENVI is using my script available here: http://www.ipgp.fr/~lucas/isis2envi.html It could be adapted and certainly improved but at least it works fine for THEMIS. Good Luck! Antoine