Dear list, Within the affy package and on a MACOSX machine (10.4.11), I want to access probe-level data on binary .CEL files (human st1 expression arrays) using the command ReadAffy, which creates an "AffyBatch" object. I get the following meassage: Error in read.affybatch(filenames = l$filenames, phenoData = l $phenoData, : Is NT_BAY.CEL really a CEL file? tried reading as text, gzipped text, binary and gzipped binary. I suspect it is a problem with the .CEL files themselves, as I don't get this on a window machine when I attempt to read the very same file. Also when I attempt to read text .CEL files, on the same MACOSX machine, I don't get that message either. So: - Is there anything I should do to modifiy those binary .CEL files to make them readable on the MAC? (chage the carriage returns for example?) - Or a way to turn a binary .CEL file into a text one? In advance, many thanks. Martino