Advances in surgical, radiation and chemotherapeutic techniques for the treatment of tumours of the CNS have not improved the prognosis of this type of cancer. Furthermore, the CNS represents a unique challenge to traditional chemotherapy because of the blood-brain barrier, the variety of tumours present within the CNS and heterogeneity within a given tumour type. Monoclonal antibody technology has provided a variety of new agents to explore as possible therapies for cancers. The use of antibodies to target isotopes, toxins, drugs or enzymes to brain tumours is currently being investigated.A number of phenomena may affect the ability of these immunoconjugates to reach the target and their efficacy once at the target site. These include tumour susceptibility and accessibility, target antigen expression, the immune response of the patient and tumour heterogeneity. We conclude, based on our research and that of others, that immunoconjugates are effective against compartmentalised tumours in the CNS, and their primary role may be in the treatment of residual disease or in combined therapeutic regimens.