Statistical properties of the HII regions of the S0 galaxies with luminosity L(Hα)≥10³⁷ erg s⁻¹ and S/N > 5. Upper left: Hα luminosity function. Upper right: relation between the Hα luminosity and the equivalent diameter. Lower left: distribution of the equivalent diameter. Lower right: distribution of the electron density. Galaxies are colour-coded as follows: Brown for NGC 4429, green for NGC 4459, red for NGC 4476, orange for NGC 4477, and blue for NGC 4526. The black histogram gives the cumulative distribution for all objects. All the Hα luminosities are corrected for [NII] contamination assuming [NII]/Hα = 0.78. Electron densities are also corrected for dust attenuation for comparison with other studies.