In this calculation we estimate the contribution of massive X-ray binaries to the hard X-ray background (XRB). Traditionally, due to their short life-times, MXRBs were thought not to be significant contributors to the XRB. However, given the recent progress in the observational determination of the global star-formation rate as a function of redshift probed both via emitted blue-light and that re-radiated in the sub-mm, assuming that the formation rate of MXRBs tracks the global star formation rate, their integrated contribution to the XRB can be computed and is shown to be non-negligible. While the origin of the bulk of the hard XRB can be attributed to obscured AGNs, we show that MXRBs can account for 10–30&percent;. ©1999 American Institute of Physics.