Initial stages of Pb deposition on Si(100) 2x1 surfaces have been studied by means of scanning tunneling microscopy, Scanning tunneling microscopy results show that, at room temperature and loa coverage. long quasi-one-dimensional Pb chains can be formed on this substrate, These chains, composed of Pb dimers, run in a direction perpendicular to the underlying Si dimer rows, The chain length suggests that Pb diffusion on the Si surface is a relevant effect even at room temperature, Some indications of Pb dimers movements are presented.