Workflow of the washing experiment: Three human genome arrays (HG-U133plus2) were hybridized with identical RNA-samples, equilibrated for 16 hours, low stringently washed and stained (labeled) using the same protocol. Stringent wash cycles and subsequent scans were applied using different protocols: Two arrays, A and B, were stringently washed and scanned in four alternating cycles where in each cycle the washing step was repeated several times as indicated. Chip C was processed using the standard protocol of six stringent washes before staining. The chip measurements are assigned according to 'chip-cycle number-(total number of washings)', e.g. A-3(7x). After finishing the first series of wash/scan-cycles the whole procedure was repeated a second time.