The structure and mechanical properties of bulk Zr50Ti16.5Cu15Ni18.5 metallic glasses were studied by X-ray diffraction, scanning and transmission electron microscopy and by measurements of mechanical properties. The transition from heterogeneous to homogeneous deformation was found to occur at 575 K. The crystallization was found to begin in the testing part of the sample earlier than in the part placed in a holder during the mechanical testing. The crystallization leads to the formation of the quasicrystalline phase with a(0) = 2.54 Angstrom, hexagonal phase ZrTi(Ni,Cu) and hexagonal phase (Zr6CoAl2 type). The difference of the structure in different parts of the sample has been observed and analyzed. The deformation does not effect on the crystallization processes occurring during the tensile testing at this temperature and the crystallization proceeds owing to the self-heating of the samples during the phase transition. The correlation between mechanical properties, structure and fracture surfaces is discussed.