Stable, irreversibly adsorbed Pt(100)-Br adlayers composed of discharged bromine atoms can be formed through vapor or electrolyte dosage. They survive emersion, can be studied in electrolytic media (either in the presence or in the absence of bromide anions), and serve as scanning tunneling microscopy samples. The voltammetric profile of Pt(LOO in acidic bromide solutions results from both hydrogen and bromide adsorption. Bromine coverages have be on measured from charge displacements under different experimental conditions, and they amount to 0.48-0.50 Br/Pt. The hydrogen adsorption contribution to the voltammetric charge in acidic bromide solutions, evaluated by charge displacement, corresponds to hydrogen coverages around 0.90 H/Pt. An ordered Pt(100)-(3 x 4)-6Br (0.5 Br/Pt) adlayer structure has been imaged, resulting from the coincidence of a distorted hexagonal Br layer (Br-Br distances between 0.38 and 0.42 nm) on the substrate net. However, for the most part of the surface it is difficult to find large, bidimensionally ordered domains. The temperature during bromine vapor dosage strongly affects the surface structure. Low temperature is required to minimize effects on the structure of the Pt(100) substrate.