Diamond layers were deposited on a Si substrate by hot-filament chemical vapor deposition from a MeH-H-2, mixt. at 2200 degrees C (W wire) and studied by Raman spectroscopy, scanning electron microscopy and electron dispersive spectroscopy for mol structure and chem. compn. The grain size in the diamond layer increased with the increasing content of MeH in the gas mixt. (1-3% by vol.).