Could someone please clarify some points about RMA normalization by confirming or correcting my summary below: 1) The background correction uses only the PM probes. Essentially, it looks for the probes below peak of the PM probe distribution, and uses these to estimate the parameters of the mixture model. 2) The quantile normalization is done on the background corrected PM probes. Thanks. I did not find the details spelled out in the papers. Naomi S. Altman 814-865-3791 (voice) Associate Professor Dept. of Statistics 814-863-7114 (fax) Penn State University 814-865-1348 (Statistics) University Park, PA 16802-2111