Dear All, I would like to plot two quantities using two different scales along the two vertical y axes. On top of this, I would like to use two different colors (let us say red and blue) for the two vertical axes, their labels, their ticks and the text for each tick. I paste below a code snippet x <- c(4,10,50,98) temp <- c(1.3e-1,4.92e-2,9.48e-3,4.84e-3) conc <- c(1.92,5.08,26.35,51.56) conc2 <- c(7.5e-1,1.14,2.12,4.7) b <- diff(range(temp))/diff(range(conc)) a <- min(temp) - b*min(conc) pdf("D_k_and_R_mobility.pdf") par(mar=c(4.5,5,2,4.2)+0.1) plot(x, temp, type="b",lwd=2,col="transparent",lty=2,xlab=expression(paste(k)) ,ann=FALSE,yaxt="none", ylim=range(c(0.,1.4e-1)), xaxt="none", xlim=range(c(0,100)),cex.lab=1.4,cex.axis=1.2) lines(x, temp, col="blue",type="b",lwd=2,lty=1,pch=2) ticks <-c(0, 0.035,0.07,0.105, 0.14) axis(side=2,at=ticks,labels=FALSE, col = "blue",cex.lab=1.4,cex.axis=1.2) mtext(side = 2, text = ticks, at = ticks, col = "blue", line = 1,cex.lab=1.4,cex.axis=1.2) mtext(side = 2, text = expression(paste(D[k])), line = 3,cex.lab=2.4,cex.axis=6.2, col="blue") ticks <-c(0, 25,50,75, 100) axis(side=1,at=ticks, labels = ticks, col = "black",cex.lab=1.4,cex.axis=1.2) lines(x, a + b*conc, col="red",type="b",lwd=2,lty=1,pch=4) lines(x, a + b*conc2, col="red",type="b",lwd=2,lty=1,pch=6) ticks <-c(0,10,20,30,40,50) axis(4, at=a + b*ticks, labels=ticks,cex.lab=1.4,cex.axis=1.2, col="red") #this controls the 4th axis and what I want to do there! mtext(expression(paste(R[g(m)])),cex=1.4, 4, 3, col="red") legend(50,0.1, c(expression(paste(D[k])), expression(paste(R[m])),expression(paste(R[g]))), lwd=c(2,2,2),lty=c(2,1,1),pch = c(1,4,6),col=c("blue", "red","red"),box.lwd=1,box.lty=1, ,xjust = 1, yjust = 1) dev.off() The result is NOT what I am looking for, since I am having a lot of troubles in tuning both the color and the size of the labels, tick locations and so on. Can anyone "fix" this example? I had a look at http://tolstoy.newcastle.edu.au/R/help/03b/2708.html and http://www.mail-archive.com/r-help at stat.math.ethz.ch/msg07033.html but obviously I am not quite there yet. Kind Regards and merry Xmas Lorenzo