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We have selected a complete sample of flat-spectrum radio quasars (FSRQs)from the WMAP 7-yr catalog within the SDSS area, all with measured redshift,and have compared the black hole mass estimates based on fitting a standardaccretion disk model to the `blue bump' with those obtained from the commonlyused single epoch virial method. The sample comprises 79 objects with a fluxdensity limit of 1 Jy at 23 GHz, 54 of which (68%) have a clearly detected`blue bump'. Thirty-four of the latter have, in the literature, black hole massestimates obtained with the virial method. The mass estimates obtained from thetwo methods are well correlated. If the calibration factor of the virialrelation is set to $f=4.5$, well within the range of recent estimates, the meanlogarithmic ratio of the two mass estimates is equal to zero with a dispersionclose to the estimated uncertainty of the virial method. The fact that the twoindependent methods agree so closely in spite of the potentially largeuncertainties associated with each lends strong support to both of them. Thedistribution of black-hole masses for the 54 FSRQs in our sample with a welldetected blue bump has a median value of $7.4\times 10^{8}\,M_\odot$. Itdeclines at the low mass end, consistent with other indications that radio loudAGNs are generally associated with the most massive black holes, although thedecline may be, at least partly, due to the source selection. The distributiondrops above $\log(M_\bullet/M_\odot) = 9.4$, implying that ultra-massive blackholes associated with FSRQs must be rare.

Black-hole mass estimates for a homogeneous sample of bright flat-spectrum radio quasars