Radium implantation has long been established as a good method for treating cancer in the anterior two-thirds of the tongue and, to a lesser extent, for other lesions of the buccal mucosa. Its advantages for healing with minimal scarring and minimal irradiation of salivary tissue are well known. The tongue lends itself well to implantation with rigid radium needles but these sources are more difficult to apply to other sites in the mouth where lesions may be confined by adjacent structures or present on curved surfaces to which the rigid sources cannot conform. For these and other reasons, in the past ten years many experiments with other radioactive sources which may be used in place of radium have been attempted. This brief paper discusses the use of tantalum 182 in the treatment of lesions of the integument generally, and of the buccal mucosa in particular. Isotopes for Interstitial Implants In recent years, many centres have been experimenting with artificial radioactive isotopes in interstitial implants in cancer therapy. Successful use has been made of cobalt 60 (1, 2), gold 198 (3, 4), iridium 192 (5), yttrium 90 (6), and tantalum 182 (7–10) for such implants in various areas of the body. The choice of a suitable isotope depends upon a number of physical and practical considerations. For implants in the region of the mouth and neck, a considerable advantage will be gained over radium if the implant is flexible and capable of following the contours of the area. Since the selected lesions are usually quite small, it is advantageous to have the length of the radioactive source adjustable in order to obtain a radiation field with optimum size and shape. Isotopes in the form of flexible wires, free seeds, or seeds mounted in plastic tubes all have this advantage. Other factors which should be considered include the half-life and availability of the isotope, the radiations emitted, and possible hazards to patients and personnel. In addition, the importance of increasing the activity around the periphery of an implant is a factor frequently ignored when artificial isotopes are used interstitially. We have found that Ta182 wire satisfies many of the requirements for a suitable isotope. Characteristics of Tantalum 182 Ta182 is easily produced by the irradiation of natural tantalum in a nuclear reactor. It decays with a half-life of one hundred and eleven days, emitting beta particles with a maximum energy of 0.52 Mev, and a wide spectrum of gamma rays. As can be seen in Table I, about 90 per cent of the radiation dose is given by a group of rays between 1.12 and 1.23 Mev, having a weighted mean energy of 1.18 Mev. The K factor for Ta182 is 6.1 r/hr./mc at 1 cm. as against 8.25 r/hr./mc for radium. With respect to the characteristics of the radiation, there is little to choose between Ta182, radium, or Co60. The tantalum is in the form of thin wires surrounded by a platinum sheath 0.1 mm. thick2 to absorb the beta particles.