Types of Mn5Ge3-based solid solutions are identified using x-ray diffraction and density measurements. In the composition range 37.0-35.0 at. % Ge, a substitutional solid solution is formed, while in the range 38.0-40.0 at. % Ge, two types of solid solutions, substitutional and deficient, are formed. Mn5Ge3 crystals are grown by the Czochralski technique.