A trial of the action of bleomycin was made on 237 cancer patients with tumours in a visible and actively growing phase who did not require surgery or radiotherapy. Bleomycin was found to have several special properties-absence of haemopoietic toxicity or immunosuppressive action and toxic side-effects affecting skin, mucosae, and lungs. The drug is more effective than drugs previously available for squamous cell carcinoma of the skin and cancer of the penis, the vulva, oesophagus, and uterine cervix, as well as for melanoma and mycosis fungoides. It is at least as effective as those drugs or combinations of drugs previously used for oropharyngeal tumours and testicular dysembryoma or choriocarcinoma. It is very effective when used in arterial perfusion therapy of otorhinolaryngeal tumours. It is of little value in other tumours, in particular for those of the haemopoietic system.