  We study photometric variability among the optical counterparts of X-ray
sources in the old open cluster M67. The two puzzling binaries below the giant
branch are both variables: for S1113 the photometric period is compatible with
the orbital period, S1063 either varies on a period longer than the orbital
period, or does not vary periodically. For the spectroscopic binaries S999,
S1070 and S1077 the photometric and orbital periods are similar. Another new
periodic variable is the main-sequence star S1112, not known to be a binary. An
increase of the photometric period in the WUMa system S1282 (AHCnc) is in
agreement with a previously reported trend. Six of the eight variables we
detected are binaries with orbital periods of 10 days or less and equal
photometric and orbital periods. This confirms the interpretation that their
X-ray emission arises in the coronae of tidally locked magnetically active
stars. No variability was found for the binaries with orbital periods longer
than 40 days; their X-ray emission remains to be explained.
