Polarized reflectance measurements have been made on two isostructural conducting compounds of bis(ethylenedithio)tetrathiafulvalene [BEDT-TTF or ET, (C10H8S8)]: β-(ET)2AuI2 and β-(ET)2I2Br. The former is superconducting at ambient pressure with Tc=5 K, whereas the latter retains normal-metal conductivity to low temperatures. The reflectance measurements, made at temperatures of approximately 30 and 300 K, spanned 80 cm-1 (0.01 eV) through 33 000 cm-1 (∼4 eV); they were made for polarization along the ET molecular stacking axis and transverse to it in the sheets or layers of ET molecules. Band-structure parameters determined from the plasmon frequencies imply that the anisotropy is rather low for organic conductors, with t?≊0.22 eV and t⊥≊0.09 eV for β-(ET)2AuI2; t?≊0.18 eV and t⊥≊0.07 eV for β-(ET)2I2Br. At 300 K, the spectra differ substantially from the expectations of simple one-electron models, suggesting that both electron-phonon and electron-electron interactions play important roles in the electronic structure of these materials. At low temperatures, the materials display basically metallic characteristics, yet deviate significantly from simple Drude-model behavior. At 30 K, no effect attributable to superconducting fluctuations could be observed.