  The 21-cm anisotropies from the neutral hydrogen distribution prior to the
era of reionization is a sensitive probe of primordial non-Gaussianity. Unlike
the case with cosmic microwave background, 21-cm anisotropies provide
multi-redshift information with frequency selection and is not damped at
arcminute angular scales. We discuss the angular trispectrum of the 21-cm
background anisotropies and discuss how the trispectrum signal generated by the
primordial non-Gaussianity can be measured with the three-to-one correlator and
the corresponding angular power spectrum. We also discuss the separation of
primordial non-Gaussian information in the trispectrum with that generated by
the subsequent non-linear gravitational evolution of the density field. While
with the angular bispectrum of 21-cm anisotropies one can limit the second
order corrections to the primordial fluctuations below f_NL< 1, using the
trispectrum information we suggest that the third order coupling term, f_2 or
g_NL, can be constrained to be arounde 10 with future 21-cm observations over
the redshift interval of 50 to 100.
