Hi guys, thanks to Jenny Drnevich I discovered how to create a boxplot of M values by print-tip group using limma package only: boxplot(MAset$M[,j]~MAset$genes$Block) Now my problem is : how to replace the xlabels (I mean, not the X-axis title) with my labels ? The default is obviously the Block number, and I would like to replace it with my vector of labels (grlab, character), the same length of the number of the boxes. Yes I know that is more an R question, and even a stupid one, but I tried in several ways and I almost became crazy on that !!! I tried with par() settings, axis(), adding "lab=", labels, tried to rename the xdata (names, rownames, etc). If someone could help me, it will be great !!! Thanks in advance, Giulio