Plotting: Plot several axis at right hand side of the plot

Hi all,

I created a graph by plotting 4 time series on top of each other but don't
know how to add extra axes on the right hand side of the plot (or leftside).
For the first two time series it axis are plotted but the last two time
series don't have and axis. How can these be added and where?

e.g.
par(mfrow=c(1,1))
    plot(timeserie1)
    par(new=T)
    plot(timeserie2, type="b", col=3,yaxt="n", ylab="" )
    axis(4)
    mtext(side=4, line=2, "NDVI")
    par(new=T)
    plot(timeserie3, type="h", col=2,yaxt="n", ylab="")
    par(new=T)
    plot(timeserie4, type="b", col=4,yaxt="n", ylab="")

Thanks,
Jan