Razoxane blocks cell division in the G2/M phase of the cell generation cycle and appears to normalize tumour neovasculature development. These were the principal reasons for the examination and probably for the demonstration of the radiosensitizing activity of Rz. Specially intriguing has been the finding that radiation of primary tumour implants in animals treated with Rz has a powerful potentiating effect on the antimetastatic activity of the combination. This concept has not yet received any clinical examination. Clinical trials with radiotherapy and Rz have demonstrated the clearest beneficial effects in terms of response rates and maintained local control in soft tissue sarcomas and possibly in recurrent rectal and in bladder carcinomas. Interesting heightened activity has also been found in hepatic metastases from gastrointestinal tumours. Carcinomas of the cervix, bronchus and head and neck, however, have not shown any benefit from the combination compared with radiotherapy alone.