Solid Freeform Fabrication (SFF) refers to techniques that create prototypes by a layer wise deposition of material. There are several techniques available, none of which allows the production of metallic prototypes without post processing, such as debinding or sintering. One of the SFF techniques, Fused Deposition Modeling (FDM(R)), is a well established process for thermoplastic materials such as for example ABS. Based on the FDM(R) technique, a process is being developed that allows the extrusion and deposition of semi-solid metals (EDSSM). The microstructure of an alloy in the semi-solid state has been investigated as a function of parameters used for rapid prototyping with SFF techniques. The extrusion and deposition processes are dependent on the rheological properties of the semi-solid metal, which in turn are dependent on the microstructure. The effect of microstructure and rheological properties on the extrusion and deposition processes is discussed.