Abstract: A method for producing three-dimensional bodies of a large number of mutually connected layers of a particle-shaped material such as a powder, and where the information of the appearance of each layer is achieved from a computer's CAD-unit or similar. An essentially even particle layer (7) of building material is applied on a support base (6) and on a masking device (9) is arranged a masking pattern in accordance with the information from the CAD-unit, which masking device is led over said particle layer and close to it. A radiation producer (8) is arranged or is led over the masking device (9), whereby the particles which are not covered by the masking pattern are exposed for radiation and thereby are attached to each other. The masking pattern is removed from the masking device and new sequences in accordance with the above are carried through until the three-dimensional body (19) is produced.