The phase diagrams of AgGaS2/AgInS2/-HgS sections in the quasi-ternary Ag2S-HgS-Ga2S3/In2S3/ systems have been constructed using differential thermal, X-ray phase and microstructural analyses. AgGaS2-HgS section is quasi-binary and belongs to the eutectic type. The coordinates of the eutectic point are 76 mol% HgS and 1018 K. AgInS2-HgS is not quasi-binary above the solidus. In the AgInS2-HgS system the limited solid solutions within the composition range 0-2 mol% HgS and 82-98 mol% HgS at 670 K were discovered. The compounds AgInS2 and HgS form limited solid solutions within the composition range 0-2 mol% HgS and 71-95 mol% HgS at 670 K. The solid solutions, in the part HgS-rich, are created on the basis of the low temperature cubic structure (a-HgS) on both sections.