Is there a way to have the affy normalization methods normalize based on a subset of predifined stable probesets... Thanks. Alex Alexander Pearlman Asst. Research Scientist New York University, School of Medicine, Human Genetics Program 550 1st Avenue, Tisch 508 New York, NY 10016 212-263-5532 (lab) 212-263-3477 (fax) 917-282-3801(cell phone)