  We present a study of the results obtained combining LO partonic matrix
elements with either LO or NLO partons distributions. These are compared to the
best prediction using NLO for both matrix elements and parton distributions.
The aim is to determine which parton distributions are most appropriate to use
in those cases where only LO matrix elements are available, e.g. as in many
Monte Carlo generators. Both LO and NLO parton distributions have flaws,
sometimes serious, for some processes, so a modified optimal LO set is
suggested. We investigate a wide variety of process, and the LO* pdf works at
least as well as, and often better than, both LO and NLO pdfs in nearly all
cases.The LO* pdf set is now available in the LHAPDF package.
