We make a quenched lattice simulation of hadron spectroscopy at beta =
6.2 with the Wilson action non-perturbatively improved. With respect
to the unimproved case, the estimate of the lattice spacing is less in
fluenced by the choice of input hadron masses. We study also the effec
ts of using an improved quark mass in the fits to the dependence of ha
dron masses upon quark masses. (C) 1998 Published by Elsevier Science
B.V.