We report a study of the Hall effect of high-purity Sr3Ru2O7 single crystals. We establish an empirical
correlation between the onset of its unusual low-temperature, high-field phase and a pronounced dip in the fielddependent Hall coefficient. Unlike the order parameter obtained from measurements of anisotropic resistivity,
which is affected by the formation of domains, the Hall effect feature seems to reflect the nature of the ordering
within a single domain. We checked for violations of the Onsager relations for the off-diagonal components
of the resistivity tensor but do not detect any. We compare our observations to those on materials that have
long-wavelength spin structures, and discuss them in relation to a growing body of theoretical work on the nature
of the low-temperature phase in Sr3Ru2O7