A complete NMR characterisation, for the isotopes ¹³⁷Ba, ⁴⁷Ti and ⁴⁹Ti, has been made for a single crystal of BaTiO₃ in the orthorhombic ferroelectric phase at room temperature. The nuclear quadrupole coupling constant and the axially anisotropic component of the chemical shift tensor have been determined for each isotope. In a variable-temperature study up to the Curie point, the nuclear quadrupole coupling constants were found to vary very nearly as the square of the spontaneous polarisation.