Dear List, I have a data set from Affymetrix experiments where the assumption of "few changes" between control and experimental samples may not hold, so global normalization may be inappropriate. I'm unsure what normalization method is best (normalizing to doped-in RNAs?), etc. Thanks. Sohail Khan Scientific Programmer COLD SPRING HARBOR LABORATORY Genome Research Center 500 Sunnyside Boulevard Woodbury, NY 11797 (516)422-4076