  We use three--integral models to infer the distribution function (DF) of the
boxy E3-E4 galaxy NGC 1600 from surface brightness and line profile data on the
minor and major axes. We assume axisymmetry and that the mass-to-light ratio is
constant in the central ~1 R_e. Stars in the resulting gravitational potential
move mainly on regular orbits. We use an approximate third integral K from
perturbation theory, and write the DF as a sum of basis functions in the three
integrals E, L_z and K. We then fit the projected moments of these basis
functions to the kinematic observables and deprojected density, using a
non-parametric algorithm.
  The deduced dynamical structure is radially anisotropic, with
sigma_theta/sigma_r ~ sigma_phi/sigma_r ~ 0.7 on the major axis. Both on the
minor axis and near the centre the velocity distribution is more isotropic;
thus the model is flattened by equatorial radial orbits. The kinematic data is
fit without need for a central black hole; the central mass determined
previously from ground-based data therefore overestimates the actual black hole
mass. The mass-to-light ratio of the stars is M/L_V = 6 h_50.
  The anisotropy structure of NGC 1600 with a radially anisotropic main body
and more nearly isotropic centre is similar to that found recently in NGC 1399,
NGC 2434, NGC 3379 and NGC 6703, suggesting that this pattern may be common
amongst massive elliptical galaxies. We discuss a possible merger origin of NGC
1600 in the light of these results.
