Comparison of the broad‐line Hβ luminosities of ULIGs and optically identified QSOs as a function of their bolometric luminosities. The data on the optical quasars are taken from Yee (1980), while the data on ULIGs with obscured broad‐line regions are from Veilleux et al. (1997). See text for a discussion of the methods used to construct this figure. The solid line represents the best log‐linear fit through the quasar data points. Given the uncertainties on the broad‐line luminosities (about 30%), only three objects from the sample of ten ULIGs with optical broad lines (NGC 7469, F11119+3257, and F11598−0112) clearly fall below the solid line and therefore appear to be powered predominantly by starbursts. The quasars are likely to be the dominant energy sources in the other ULIGs.