<p>Near-threshold spectra of Rydberg and autoionization states of the thallium atom have been studied by the method of selective stepwise photoionization of atoms with laser radiation. A so-called “transparency window” of width 25 ± 2 cm⁻¹, the center of which was 45 cm⁻¹ higher than the boundary of thallium atom ionization (<i>E</i>_<i>i</i> = 49,266.71 cm⁻¹), was found in the ionization continuum near the threshold. The formation of this window was evidently connected to the sharp and deep asymmetry of the previously discovered Beutler–Fano autoionization resonance having the configuration 6<i>s</i>6<i>p</i>^{2 4}<i>P</i>_3/2, situated 659 cm⁻¹ higher than the ionization boundary (<i>E</i>_0.5 = 49,925.70 cm⁻¹). The autoionization resonance contour had such a profile that Fano parameter (<i>q</i>) on the long-wavelength continuum side approached zero. This probably happened because of the strong interaction of the level with the continuum.</p>