This certainly did the trick, Thanks Ted, Sean, Romain, Dimitris, Lian and Andy, > alnlength<-rchisq(1000,4) > x<-0.25*(0:100) > hist(alnlength,breaks=0.25*(0:100)) > lines(x,1000*dchisq(x,4)*0.25) And apologies for my "newbieness" in the posting, Albert.