In this paper a complex study of the capabilities of Particle-Induced X-ray Emission (PIXE) technique for the determination of major, minor and trace constituents of metallurgical, biological and environmental samples has been done. PIXE analyses have been carried out using a 3 MeV proton beam generated with the aid of the 7 MV FN tandem accelerator of the "Horia Hulubei" National Institute of Physics and Nuclear Engineering (NIPNE) Bucharest. The detection system included a GeHP detector with an energy resolution of 170 eV at 5.9 keV for the X rays. The targets were mounted in the irradiation chamber at 45 degrees with respect to the beam and the detector's direction. A thin surface barrier silicon detector was also placed in the chamber, at 135 degrees with respect to the beam direction, in order to detect the backscattered protons for spectra normalization. The X-ray and particle spectra were simultaneously collected and processed offline. The elements identified in the metallurgical samples (steels) using PIXE were: K, Ca, V, Cr, Mn, Fe, Co, Cu, Ni, Zn, W, Ga, As, Pb, Mo, Rb, In, Rh, Zr, Pd, Nb, Sn and Sb. In the investigated biological and environmental samples (vegetables leaves, soil and mosses) PIXE analysis allowed determination of: S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Hg and Pb.