I have the following problem. Analysing affymetrix data I calculated euclidean distances between samples and visualized the results in a heatmap. Prior data were vsn normalized. heatmap(as.matrix(dist(t(exprs(TGF_eset.vsn[(tvlist),])))), col=colourRamp) Depending on the memory I assign to R (512MB, 1024MB, 1536MB) I get slightly different results. Exactly the same scripts were used. Although main results remain in the detail I have differences. Is there any explanation for these results? thanks for the help Thomas Zander Dr. Thomas Zander MTBTI, HS16UG Dept. of Internal Medicine I Universit??tsklinik K??ln Joseph-Stelzmannstr. 9 D-50924 K??ln Germany Tel.: +49-221-4784447/ 4785413 Fax: +49-221-4783647 Thomas.Zander at uk-koeln.de