The optical transmission of a xenon flashtube has been measured at wavelengths from 2500 to 10 000 Å and at currents up to 5000 A/cm2. It is found that the absorption increases with current and with wavelength. Above about 5000 Å and a current of 4000 A/cm2, a discharge tube 1 cm thick is nearly opaque. At shorter wavelengths or lower currents, the discharge is fairly transparent.