We have presented the results of an optical and radio monitoring campaign on the BL Lac object AO 0235+164 during a faint state. Large amplitude (up to three magnitudes) variations were observed in the optical bands. At radio frequencies the behaviour has been less dramatic. An inspection of the historical and current data suggests that there are at least two different processes involved in the optical emission of this blazar. One of them would be responsible for the similar general trends in the optical and radio bands and could be identified with the synchrotron process in the relativistic jet. On the other hand, the optical flares not showing radio counterparts could be due to a microlensing effect by a foreground galaxy. A further observational effort is required in order to shed light on this issue.
Part of the observations presented here were taken during the 5% international time on the Canary Island telescopes awarded to the OJ-94 Project. This work was partly supported by the Finnish Academy of Sciences.