We present multifrequency, quasi-simultaneous spectra for a sample of 11 blazars. The spectral shape of the violently variable millimeter to ultraviolet flux is consistent with emission from a very compact single component which becomes self-absorbed at wavelengths longer than ~ 3 mm. The centimeter emission can be attributed to a separate, more slowly varying component. Three out of four optically violent variable (OVV) quasars also exhibit evidence of a "UV excess" component. Throughout the millimeter-UV region, the flattest spectral slopes, observed when the sources are bright, are all close to -0.7. However, the steepest slopes (observed when the sources are fainter) become steeper as one progresses to shorter wavelength. We interpret this in terms of successive injections or reaccelerations of electrons in a flaring component, superposed on the more slowly varying component which peaks at centimeter wavelengths. We deduce values for the size of the flaring regions of 10^-3^-10^-1^ pc and magnetic fields of order 1 G. We also deduce that photon energy densities may dominate over magnetic field energy densities, in which case inverse Compton scattering may be the dominant energy loss mechanism in the flaring components.
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Brown et al. (1989) studied this question.