  We present improved visual and near-infrared empirical mass-luminosity
relations for very low mass stars (M$<$0.6~\Msol). These relations make use of
all stellar masses in this range known with better than 10% accuracy, most of
which are new determinations with 0.2 to 5% accuracy from our own programme,
presented in a companion paper.
  As predicted by stellar structure models, the metallicity dispersion of the
field populations induces a large scatter around the mean V band relation,
while the infrared relations are much tighter. The agreement of the observed
infrared mass-luminosity relations with the theoretical relations of Baraffe et
al. (1998) and Siess et al. (2000) is impressive, while we find an increasingly
significant discrepancy in the V band for decreasing masses. The theoretical
mass-luminosity relation which is insufficiently steep, and has introduced some
errors in the local stellar mass functions derived from V band luminosity
functions.
