We report on our search for very-long-term variability ( weeks to years ) in X-ray binaries ( XRBs ) in the giant elliptical galaxy M87 .
We have used archival Chandra imaging observations to characterise the long-term variability of 8 of the brightest members of the XRB population in M87 .
The peak brightness of some of the sources exceeded the ultra luminous X-ray source ( ULX ) threshold luminosity of \sim 10 ^ { 39 } erg s ^ { -1 } , and one source could exhibit dips or eclipses .
We show that for one source , if it has similar modulation amplitude as in SS433 , then period recoverability analysis on the current data would detect periodic modulations , but only for a narrow range of periods less than 120 days .
We conclude that a dedicated monitoring campaign , with appropriately defined sampling , is essential if we are to investigate properly the nature of the long-term modulations such as those seen in Galactic sources .