Similarly to what can be read on help(qqplot), however using Rayleigh distribution: library(VGAM) p <- ppoints(100) x <- qrayleigh(p) y <- rrayleigh(100) qqplot(x,y) qqline(y, distribution = function(p) qrayleigh(p), prob = c(0.1, 0.6), col = 2) -- GG [[alternative HTML version deleted]]