  Long exposure observations at the Canada-France-Hawaii Telescope of 3C66B in
the I filter are presented. After subtraction of the galactic background,
optical emission on the counterjet side is detected in 10 knots coincident with
the radio counterjet. Their radio-to-optical spectral indices (0.5--0.6) are
typical of synchrotron emission in extragalactic jets, so that these knots
possibly are the optical counterparts of the radio counterjet. If this is
confirmed, 3C66B would be the first double-sided extragalactic optical jet. The
optical counterjet would also be brighter than what is predicted from the
relativistic beaming interpretation of brightness asymmetry between the two
jets. This would thus prove that the radiation properties are intrinsically
different in the two jets. Alternatively, these knots could have nothing to do
with the counterjet. But it seems that in this case, the optical counterjet
would be fainter than expected from the relativistic beaming interpretation,
favouring intrinsic asymmetry as well. In addition, two new optical components
are found in the jet.
