xyplot(Y~X,groups = TRT,type=n) to plot the space but not the points, then use the text function to display the characters. Try ?text in R -- View this message in context: http://r.789695.n4.nabble.com/Plot-using-treatment-letter-as-points-tp3276743p3276775.html Sent from the R help mailing list archive at Nabble.com.