Results from therapeutic trials with radiolabelled monoclonal antibodies are difficult to compare, because of lack of accurate macroscopic and microscopic dosimetry for both tumours and normal tissues. Requirements for such a dosimetry are covered in the paper. Accurate in vivo dosimetric measurement techniques for verification of calculated absorbed doses are also needed to verify treatment planning. In the review, important topics related to dosimetry in therapeutic trials in RIT are covered, such as, absorbed-dose calculations and activity-quantification techniques for planar imaging and SPECT. The latter is particularly discussed, including a summary of different correction techniques. Absorbed-dose calculations and treatment-planning techniques are also discussed. Possible ways of enhancing the therapeutic ratio are reviewed, especially the novel technique with extracorporeal immuno-adsorption. The review could form the basis of the development of future treatment-planning protocols and for dosimetry calculations in radio-immunotherapy, considering some of the most important parameters for approaching an accurate in vivo dosimetry.