Tom, Thank you for your quick reply. I have indeed looked at using Amira to segment our data, but currently we do not have the resources to purchase it with all the necessary modules. You have a good point about the possibility of removing too much data when trying to separate features by altering the threshold. My initial plan was to use the tools in a multi step process: The first step would be to use a crude threshold that selects the features of interest plus extra voxels. This step should hopefully eliminate many of the small particles that fill the tomograms (it could also be used to eliminate larger objects that you may not interested in, such as ribosomes when looking at intracellular structures). The idea was to use this crudely selected data set to find better thresholds with which to examine the features of interest. This should be made easier because there would be fewer small (1-2 voxel) particles crowding the view. A problem I can foresee is that the pick surface pieces currently surrounds the voxels on all surfaces, ie it can turn voxels surrounding a stick-like structures into tubes. To be able to use this method effectively the program would have to select the entire volume surrounded by the outer surface. I accept that this is probably quite a rough and ready way of segmenting the data, but it strikes me as a quick method of removing unconnected data from the features of interest that is less prone to human error than using the volume eraser. Thanks for the information on the bondzone. This feature seems useful. A quick extra question. Is it possible to increase the effective radius of colourzone? I have a data set with a voxel size of 1 nm cubed, so the current maximum radius of 30 angstroms only selects a radius of 6 voxels. I can reset the effective voxel size, but this makes the images look odd due to the large magnifications needed. Thanks again for all the help. TobyS -- Dr T Starborg FLS, University of Manchester Michael Smith Building, Rumford Street, Manchester,M13 9PL. UK tel:+44(0)161 275 1557 fax +44(0)161 275 1505