Molybdenum and tungsten thin films were deposited onto MgO(100) and amorphous substrates (silica, glass) by d.c.-sputtering in argon. Although the gas used is neutral, the deposits realized for both metals with low deposition rates v(d) (< 6 nm min-1) presented an f.c.c. structure. The occurrence of this structure was independent of the substrate nature. A detailed study concerning molybdenum showed that for v(d) > 6 nm min-1, Mo systematically appeared in the bulk b.c.c. structure. It is proposed that the f.c.c. structure is stabilized by metalloid impurities (C, N, O) present in the residual atmosphere. Special care was given to the orientation of the Mo and W f.c.c. layers on MgO(100), and a (100) orientation was observed. It was found that these deposits exhibit, under certain conditions, the same orientation on amorphous substrates, which is characteristic of a fiber texture of [100] axis. The crystallographic structure of the coatings was explored by X-ray, RHEED and THEED techniques. Surface composition was determined by AES.