ENVI format files are just flat binary files, with an associated ASCII header file that provides information needed to correctly interpret the image within the binary file (number of columns, rows, bands, etc.). So, you can open the binary file containing the data using IDL's OPENR routine. To read the data from the file into an IDL array (assuming that you have enough RAM to do that), you could use the IDL routine READU. It sounds like your hyperspectral file is going to be far too large to read into an array in RAM. So, in that case, you will need to read only a part of it at a time. Interactive ENVI automatically implements tiling in these cases. You'll want to do something like that in your IDL code as well. If you have access to ENVI + IDL, then you will probably want to look at the ENVI routine ENVI_OPEN_FILE, and use that in your IDL code. ENVI opens files in a different way than IDL. ENVI's way is designed to make calling ENVI routines, which often implement tiling automatically, easier for large datasets. I hope that helps. - Peg