We have made an extensive study of the magnetic and electrical properties of double-hexagonal close-packed NpPd(3) and a range of (U(1-x)Np(x))Pd(3) compounds with x=0.01, 0.02, 0.05, and 0.50 using magnetization, magnetic susceptibility, electrical resistivity, and heat capacity measurements on polycrystalline samples, performed in the temperature range 2-300 K and in magnetic fields up to 9 T. Two transitions are observed in NpPd(3) at T=10 and 30 K. Dilute Np samples (x <= 0.05) exhibit quadrupolar transitions, with the transition temperatures reduced from those of pure UPd(3).