  The properties of the few symbiotic stars detected among the 66 binary S
stars from the Henize sample are discussed. Two stars (Hen 18 and Hen 121)
exhibit both a strong blue-violet continuum and strong H_alpha emission (FWHM
of 70 km/s), whereas Hen 134 and 137 exhibit weak H_alpha emission. The H_alpha
profiles are typical of non-dusty symbiotic stars belonging to class S-3 as
defined by Van Winckel et al. (1993, A&AS 102, 401). In that class as in the
Henize symbiotic S stars, He I, [N II] or [S II] emission lines are absent,
suggesting that the nebular density is high but the excitation rather low. The
radial velocity of the centre of the H_alpha emission is identical to that of
the companion star (at least for Hen 121 where this can be checked from the
available orbital elements), thus suggesting that the H_alpha emission
originates from gas moving with the companion star. For Hen 121, this is
further confirmed by the disappearance of the ultraviolet Balmer continuum when
the companion is eclipsed by the S star. Hen 121 is thus the second eclipsing
binary star discovered among extrinsic S stars (the first one is HD 35155). A
comparison of the available data on orbital periods and H_alpha emission leads
to the conclusion that H_alpha emission in S stars seems to be restricted to
binary systems with periods in the range 600 - 1000 d, in agreement with the
situation prevailing for red symbiotic stars (excluding symbiotic novae).
Symbiotic S stars are found among the most evolved extrinsic S stars.
