Full-dimensional first dipole hyperpolarizability surfaces of NH3 are determined by means of multiconfigurational quadratic response theory. On the basis of the two-dimensional, symmetric stretching vs inversion, hyperpolarizability functions, and approximate vibrational wave functions, effective inversional hyperpolarizability moments are evaluated for the D3h ammonia isotopomers. The calculations have revealed their strong vibrational and frequency dependence. A fairly close reproduction of the first hyperpolarizability ESHG constant beta (632.8 nm) by theory indicates that the major correction to the one-particle hyperpolarizability is obtained by variational wave functions including a comparatively small set of active orbitals. We find that a meaningful comparison with experimental results can only be obtained by an appropriate evaluation of both the vibrational and the correlated dispersion dependencies.