[en] Polycrystalline samples of Hg_2x(AgIn)_1-xTe₂ alloys are prepared by the melt and anneal technique. Differential thermal analysis (DTA) measurements are carried out on the alloys and the T(x) diagram determined. Guinier X-ray powder photographs are used to show the equilibrium conditions and to give lattice parameter values. Only two single phase solid fields, the zinc blende and chalcopyrite fields are found to exist in the diagram. The form of the solidus curve bounding a wide two-phase liquid plus solid field shows that the section is not pseudobinary. Microscopic and DTA data show the presence of the dissociated phase in the grain boundaries of the zinc blende phase at temperatures below 400 ⁰C. (author)