  We present an analysis of high resolution spectra in the J band of five ultra
cool dwarfs from M6 to L0. A new ab initio water vapour line list and existing
line lists of FeH and CrH were used for spectra modelling. We find a good fit
for the Mn I 12899.76 A line. This feature is one of the few for which we have
a reliable oscillator strength. Other atomic features are present but most of
the observed features are FeH and water lines. While we are uncertain about the
quality of many of the atomic line parameters, the FeH and CrH line lists
predict a number of features which are not apparent in our observed spectra. We
infer that the main limiting factor in our spectral analysis is the FeH and CrH
molecular spectra.
