Light hadron spectrum and light quark masses from lattice QCD

We present recent results on the light hadron spectrum and light quark mass es in lattice QCD, both in the quenched approximation and with two flavors of dynamical quarks. Simulations are made with a renormalization-group impr oved gauge action and a tadpole-improved clover quark action. Our new resul ts in the quenched simulation are in good agreement with our previous calcu lation using the standard lattice action. A comparison between the results in full and quenched QCD clearly shows the existence of sea quark effects i n meson and quark masses.