I have a set of custom spotted arrays that were manufactured using different 8 print tips, where each print tip spotted probes for 6 subgrids. There are 12 rows and 4 columns of subgrids, with each subgrid containing 21 x 21 spots. After reading the data using, for example, > brain.layout<-read.marrayLayout(fname=chip7.12,ngr=12,ngc=4,nsr=21,nsc =21,skip=21211) > brain.gname<-read.marrayInfo(chip7.12,info.id=c(1,6),labels=6,skip= 21211) > brain.raw<-read.marrayRaw(chip7.12,name.Gf="ch1Intensity",name.Gb="ch1 Background",name.Rf="ch2Intensity",name.Rb="ch2Background",layout=brai n.layout,gnames=brain.gname,skip=21211) I used the marrayNorm function maNorm to normalize by PrintTip, but the default seems to consider each subgrid as being printed by a different print tip (thus there are 48). How can I change the print tip assignment so that the actual print tip is used rather than those calculated by calling maPrintTip? maPrintTip does not seem to be a slot anywhere. Thanks. Regards, Kellie J. Archer, Ph.D. Assistant Professor, Department of Biostatistics Virginia Commonwealth University 1101 East Marshall Street Richmond, VA 23298-0032 kjarcher@vcu.edu