Various types of ground states in strongly correlated electron systems have been systematically investigated by means of NMR/NQR at low temperatures under high magnetic field and pressure. We focus on two well-known heavy-electron families, CeCu2X 2 (X = Si and Ge) (Ce(122)) and UM2AI 3 (M = Ni and Pd) (U( 123)). The Cu NQR experiments on CeCu2X 2 under high pressure indicate that the physical property of CeCu2Ge 2 at high pressure, i.e. above the transition at 7.6GPa from antiferromagnetic (AF) to superconductivity, are clearly related to that of CeCu2Si 2 at ambient pressure. In addition to the H-T phase diagram established below 7 T, NMR and specific heat experiments on polycrystal CeCu2.05Si 2 have revealed the presence of a new phase above 7 T. In a high-quality polycrystal of UPd2AI 3 with a record high-T c of 2 K at ambient pressure and the narrowest AI NQR line width, the nuclear-spin lattice relaxation rate, 27(1/T~) measured in zero field has been found to obey the T 3 law down to 0.13 K, giving strong evidence that the energy gap vanishes along lines on the Fermi surface. Thus it seems that all heavy-electron superconductors exhibit lines of zero gap, regardless of their different magnetic properties.