The spin-echo response of interacting pairs of spin-³/₂ quasi-particles is calculated for 90 degrees - tau - beta _{90 degrees} sequences. The calculation is aided by the introduction of spin manifolds of different spin character; each manifold may be considered separately. No truncation of the dipolar interaction is performed; the calculation is in the representation in which the entire Hamiltonian is diagonal. The authors' results may be compared with the numerical calculations of Baianu et al. (1981) and their experimental results for spin-¹/₂ triads. It is found that there is reasonable but not perfect agreement with experiment, and it is suggested that the interacting quasi-particle model may not be absolutely valid for this system.