Beta-21S titanium alloy is ranked among the most important advanced materials for a variety of technological applications, due to its combination of a high strength/weight ratio, good corrosion behavior and oxidation resistance. However, in many of these technological applications, this alloy is exposed to environments which can act as sources of hydrogen, and consequently, severe problems may arise. The objective of this paper is to investigate the influence of high fugacity hydrogen on Beta-21S alloy in as-received (mill-annealed and hot-rolled) condition. Hydrogen effects on the microstructure are studied using X-ray diffraction and electron microscopy, while the absorption and desorption characteristics are determined respectively by means of a hydrogen determinator and thermal desorption spectroscopy. Preliminary results at room temperature revealed hydrogen-induced straining and expansion of the lattice parameters. However, neither second phases formation (hydrides), nor hydrogen-induced cracking, were observed after hydrogenation. The main characteristics of hydrogen absorption/desorption behavior, as well as hydrogen-induced microstructural changes in both microstructures are discussed in detail.