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If Wayne is even close on the size of your direct dimension, Ičll second his suggestion to trim it down, in many bioNMR experiments signal decays in the first 600-800 complex points or so of the FID anyway. 2k points usually gives enough resolution for most anything I need, occasionally Ičll extend a 2D to 4k. Also, if youčre not converting to a blocking data format like Justin mentioned, youčll have problems. With 2007-vintage computers, larger 3D datasets become painful if kept in NMRPipe format (and almost unusable if you want to display XZ or YZ instead of XY). Ičd strongly suggest that once you find a reasonable contour level for your 4D NOESY and then let Analysis create contour files for the spectrum: Experiment->Spectra, choose the Display Options tab, select you spectrum, click Contour Files, in the new window click Create New File, choose your 4D and the two dimensions you plan to view most of the time, then click Contour and Save. This should greatly speed up scrolling and redrawing since otherwise the software calculated the contours on the fly, although if you want to adjust contours at a particular place youčll need to toggle using the contour file on and off in the Display Options tab. If youčll be looking at an orthogonal view more than occasionally, youčll need to make contour files for each pair of two dimensions you plan to look at. For a large 3D creating a contour file can take several minutes, so Ičd start contouring before you go home for the day. The files will be large. Also, avoid scrolling as much as possible. Since youčre looking at a 13C,15N edited NOESY, two dimensions will be the same as your 15N HSQC. View the other two dimensions of your 4D and go through one HSQC peak at a time. As a last resort if the data is still painful to work with, you can do what I had to do with a large (>2 GB) 3D 13C NOESY under 32-bit Analysis and break your 4D up into multiple spectra. Exactly where will be up to both your personal preference and the data. Ičd suggest about 4-8 chunks. In my case, I processed the data with NMRPipe twice and extracted different 13C regions (aliphatics vs. aromatics, and threw away about 30 ppm of 13C with no signals). Keep in mind that as far as Analysis is concerned, these will all be separate spectra and youčll have to combine the peak lists later. Andrew ________________________________ Notice: This UI Health Care e-mail (including attachments) is covered by the Electronic Communications Privacy Act, 18 U.S.C. 2510-2521 and is intended only for the use of the individual or entity to which it is addressed, and may contain information that is privileged, confidential, and exempt from disclosure under applicable law. If you are not the intended recipient, any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately and delete or destroy all copies of the original message and attachments thereto. Email sent to or from UI Health Care may be retained as required by law or regulation. Thank you. ________________________________