Hi, I have tried masking particular probepairs with mas5, expresso,and computeExprSet, but find in all cases that the probesets with the masks get "NA" expression values. In other words, I am unable to mask probepairs without masking the whole probeset. Earlier mail seemed to indicate that the masked probepairs worked. Does anyone think that I am doing something wrong? With RMA I get some NA's but do get some probeset expression values. Thanks, Lana [[alternative HTML version deleted]]