  We present radial velocity and photometry for four early-type, massive
double-lined spectroscopic binaries in the R136 cluster. Three of these systems
are eclipsing, allowing orbital inclinations to be determined. One of these
systems, R136-38 (O3 V + O6 V), has one of the highest masses ever measured, 57
Mo, for the primary. Comparison of our masses with those derived from standard
evolutionary tracks shows excellent agreement. We also identify five other
light variables in the R136 cluster which are worthy of follow-up study.
