Unwanted convergence of interstitial needles may result from incorrect appreciation of their position in the tumor. Coaxial inserters (those whose axes are the same as those of the needle) obviate this miscalculation since they reveal by their position the spatial distribution of the needles. The insertion of subsequent needles can thus proceed without interruption, resulting in faster insertions and less exposure. Another advantage is that, since the pressure that drives the needle into the tissues is exerted along its axis, accidental bending is unlikely. Instrument and Technic The coaxial radium-needle inserter described here is an adaptation of the draftsman's lead-holder. It resembles a ball-point pen, but the point end has a four-prong device which opens to receive the needle when the plunger on the other end is depressed. When the plunger is released, the instrument grasps the radium needle quickly and tightly. It can be released by again pressing on the plunger. The instrument is cheap, readily available, all metal, spring-operated, and easy to disassemble, clean, and sterilize. Gas sterilization is preferable. Where this is not available, an autoclave may be employed. With an autoclave, however, the paint should be removed by means of paint remover, as it tends to be chipped from the holders by heat. When holding a radium needle, this instrument in effect becomes an extension of the axis of the needle (Fig. 1). When the needle is introduced into the tissues, this extension remains as a guide, indicating its position and alignment. The insertion of the next and subsequent needles is then guided by the position of the ones already in the tissues. With enough inserters, if the implant requires several planes of needles, each plane or row of inserters is left in place until the adjacent row has been introduced. As with any radium-needle inserter, the needle should be introduced into the tissues by applying pressure along the axis of the inserter to avoid damage to the needle. Attempts to use the needle as a lever to lift or to otherwise apply force to the tissues may result in its bending or breaking, a dangerous accident. The volume or area to be implanted and the point of entrance of the needles should be marked on the skin with a suitable ink before the insertion begins. A dummy needle may be employed to pierce the skin at all the points of entrance before introducing any radium. This eliminates exposure during the delay that may result from attempts to penetrate the skin. For particularly hard tumors, one inserter may be loaded with a dummy needle and used to bore a hole through the tumor for the easy insertion of each radium needle. The dummy needle and holder should be distinctly labeled to avoid the possibility of confusing it with a radium needle.