I would like to make a mixed environment for the mouse U74B (and C separately) version 1 and 2 chip set using common probesets. I know Ben Bolstad has built such a mixted environment for the U74 A chip. How do you do this? There are 5 library files for each chip. Do I have to create new library files containing only the common probesets and then using the make.cdf.package? I would be grateful for suggestions on how to proceed. Juerg Straubhaar Umass Med School