Modelling of atomic structures and shape analysis MASSHA is a 3D graphic system to display and manipulate atomic structures and low resolution models. The program is coupled with computational modules to allow interactive and automated rigid body refinement against solution scattering data. MASSHA is compiled using Compaq Visual Fortran v. 6.6B with QuickWin graphics library and runs under MS Windows 95/98/NT/2000/XP/Vista or under Windows emulators (like WINE) installed on Linux/MAC.