superimpose density line over hist

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.