In reviewing the current state of affairs in radioimmunotherapy the paper focuses on the main difficulties thus far encountered and the procedures designed to avoid or circumvent these problems. The long range beta-emitters 90Y and 188Re have replaced 131I as the isotopes currently receiving most attention for use in radioimmunotherapy, and a range of new chelators are under investigation for in vivo stability and immunogenicity. Approaches aimed at improving tumour targetting and antigen expression such as two-step pretargetting techniques, tumour necrosis treatment and cytokine pretreatment are summarized. Methods designed to improve host-Mab interactions are outlined and the need to incorporate successful ideas from current cancer therapies is emphasised.