  We have analysed an XMM-Newton observation of the low mass X-ray binary and
atoll source MXB 1728-34. The source was in a low luminosity state during the
XMM-Newton observation, corresponding to a bolometric X-ray luminosity of
5*10E36 d^2 erg/s, where d is the distance in units of 5.1 kpc. The 1-11 keV
X-ray spectrum of the source, obtained combining data from all the five
instruments on-board XMM-Newton, is well fitted by a Comptonized continuum.
Evident residuals are present at 6-7 keV which are ascribed to the presence of
a broad iron emission line. This feature can be equally well fitted by a
relativistically smeared line or by a self-consistent, relativistically
smeared, reflection model. Under the hypothesis that the iron line is produced
by reflection from the inner accretion disk, we can infer important information
on the physical parameters of the system, such as the inner disk radius, Rin =
25-100 km, and the inclination of the system, 44{\deg} < i < 60{\deg}.
