  We observed three AGN from the Parkes Half-Jansky Flat-spectrum Sample at
near-infrared (NIR) wavelengths to search for micro-variability. In one source,
the blue quasar PKS 2243-123, good evidence for NIR micro-variability was
found. In the other two sources, PKS 2240-260 and PKS 2233-148, both BL
Lacertae objects, no such evidence of variability was detected. We discuss the
implications of these observations for the various mechanisms that have been
proposed for micro-variability.
