X-ray powder diffraction, differential thermal analysis DTA and magnetic susceptibility chi measurements were carried out on polycrystalline samples of the alloy system MnIn2(1-z)-Ga-2,Se-4. Magnetization measurements at 2 K in magnetic fields up to 35 T were made on the MnIn2Se4 and MnGa2Se4 compounds. From the lattice parameter values, the limits of single-phase solid solution were estimated. At room temperature, the solid solutions extend over the range 0 < z < 0.30 for the delta-phase and from 0.75 to 1.0 for the eta-phase. Values of T-N, the Neel temperature, were obtained from the cusp in the chi versus T curves. Values of Curie-Weiss temperature theta were determined from the 1/chi versus T curves for the single-phase samples in each range. The magnetic results indicate that for 0 < z < 0.30, the Mn is randomly distributed over the cation sublattice, the phase having space group R (3) over barm and the compound Mnln(2)Se(4) (z = 0) was found to be spin-glass, with T-g = 2.75 K and theta = -94 K. The high z single phase eta alloys show an ordered distribution of the Mn2+ ions on the cation sublattice and were antiferromagnetic showing ideal Curie-Weiss behavior, with TN = 8 K and the Curie-Weiss temperature theta =-24 K. (C) 2002 Elsevier Science Ltd. All rights reserved.