I would like to do as follows plot(a,b) points(c,d,pch=19) Now join with a line segment point a[1], b[1] to c[1], d[1]; a[2], b[2] to c[2], d[2] ... a[n], b[n] to c[n], d[n] All corresponding points from the two data sets are joined by line segments. Thanks very much for any tips on how to do this. Bill