Pure rotational spectra of six isotopomers of the rare gas trimer Ne-2-Kr and five isotopomers of the trimer Ne-2-Xe have been measured in their ground vibrational states using a Balle-Flygare-type cavity pulsed microwave Fourier transform spectrometer. Rotational constants have been evaluated, from which the geometries of the complexes have been derived. In the case of Ne-2-Kr it has been possible to obtain centrifugal distortion constants and to carry out a force field analysis. The magnitudes of the induced dipole moments of these trimers have been estimated from the "pi/2 condition." The nuclear quadrupole hyperfine patterns due to Kr-83 and Xe-131 have been resolved, and the corresponding quadrupole coupling constants have been obtained. Observation of the spectra of these fundamental trimers has made it possible to compare their properties to those of their constituent rare gas dimers. The effects of three-body nonpairwise additive forces have been discussed in light of the structures obtained, the estimated induced dipole moments, and the nuclear quadrupole coupling constants.