We report ultrahigh vacuum scanning tunneling microscopy (UHV-STM) study of the atomic hydrogen adsorption onto a clean Si(113)-3 × 2 surface on an atomic scale. Even after hydrogen exposure of 4 L, STM images reveal clearly that some adatoms are invisible and some pentamers change their image contrast, probably due to hydrogen adsorption at the surface dangling bonds of the corresponding sites. Based on the results of STM together with low-energy electron diffraction (LEED), we discuss the initial adsorption processes of atomic hydrogen on Si(113)-3 × 2 and the transition from 3 × 2 to 3 × 1. [DOI: 10.1380/ejssnt.2005.263]