  We analyse the possible role of new interactions of neutrino in the
forthcoming tritium beta decay experiment KATRIN aimed at detecting the
neutrino mass with the sensitivity of 0.3 - 0.2 eV. It is shown that under
certain circumstances the standard procedure of data analysis would have to be
modified by the introduction of an extra parameter describing the strength of
the new interactions. Our model simulations show that the modified procedure
may improve the quality of the fit compared with the standard case. Ignoring
the possibility of new interactions may lead to a systematic error in the
neutrino mass determination.
