ZnS monocrystals, grown by solid-phase recrystallization SPR during hot pressing in the phase transition (PT) region are shown to have been improved by the doping of In. SPR of undoped and Al- or Ca-doped ZnS has not been successful. X-ray Laue patterns of as-grown ZnS monocrystal showed cubic symmetry. Scanning electron microscope investigation of the boundary surface between the monocrystalline and the polycrystalline parts of the as-grown ZnS:In ceramic disk showed an abnormal growth of crystallites into a monocrystal. To explain the role of In, high-temperature electrical conductivity (HTEC) measurements were performed. The temperature region from 1000 degrees C to 500 degrees C on the HTEC isobar of ZnS:In monocrystal was "cleared" from step-like PT changes, obligatorily observed on isobars of undoped and Cu-doped ZnS isobars in this region.