We investigated the zero-phonon line (ZPL) of the deep donor EL2 in GaAs by means of high-resolution absorption spectroscopy with a narrow-band laser. Frequency-selective bleaching (``spectral-hole burning'') experiments and the measurement of the temperature broadening of the ZPL prove an essentially homogeneous broadening of the transition. The observed asymmetry of the line shape is interpreted to be caused by a Fano resonance of the
1T2 excited state with the conduction band. A splitting of the
1T2 state as the reason for the asymmetry seems unrealistic. The homogeneous broadening of the ZPL prevents the use of spectral-hole burning spectroscopy to study the effect of external perturbations on the ZPL of the EL2.