Hi there, I'm new on the list. I am wondering as how to make different q-q plots and display them on the same scale in order to attain an easy visual comparison. I have tried to use xlim and ylim as arguments to qq.plot in a similar fashion to what is done on plot, also I have tried to use the plot.window utility to implement xlim and ylim. I have even modified the qq.plot.R source and re-compiled but none of these efforts has given any result. I am doing a sequence of steps like the following: library(car) p<-read.csv("inputP",header=T) p <- apply(p,c(1,2),as.numeric) q<-qchisq(1-p,2) png(file="outputP.png", bg="transparent") plot.window(xlim=c(0,50), ylim=c(0,50)) qq.plot(q, dist="chisq", df=2) y<-rchisq(length(p),2) lines(y,y) dev.off() Is there anything that I can do to produce several q-q plots from different data and put them in the same scale, say x-values in (0-50) and y-values in (0-50)? Thank you to all in advance -- Dr. Enrique Hern?ndez Lemus Medical Sciences Researcher "B" Computational Genomics Phone: 5350-1970 Fax: 5350-1999 Email: ehernandez at inmegen.gob.mx