  We present a method that we developed to discern where the optical
microvariability (OM) in quasars originates: in the accretion disk (related to
thermal processes) or in the jet (related to non-thermal processes). Analyzing
nearly simultaneous observations in three different optical bands of continuum
emission, we are able to determine the origin of several isolated OM events. In
particular, our method indicates that from nine events reported by Ramirez et
al. (2009), three of them are consistent with a thermal origin, three to
non-thermal, and three cannot be discerned. The implications for the emission
models of OM are briefly discussed.
