  New spectroscopic observations of the LBV/WR multiple system HD5980 in the
Small Magellanic Cloud are used to address the question of the masses and
evolutionary status of the two very luminous stars in the 19.3d eclipsing
binary system. Two distinct components of the N V 4944 A line are detected in
emission and their radial velocity variations are used to derive masses of 61
and 66 Mo, under the assumption that binary interaction effects on this atomic
transition are negligible. We propose that this binary system is the product of
quasi-chemically homogeneous evolution with little or no mass transfer. Thus,
both of these binary stars may be candidates for gamma-ray burst progenitors or
even pair instability supernovae. Analysis of the photospheric absorption lines
belonging to the third-light object in the system confirm that it consists of
an O-type star in a 96.56d eccentric orbit (e=0.82) around an unseen companion.
The 5:1 period ratio and high eccentricities of the two binaries suggest that
they may constitute a hierarchical quadruple system.
