Throughout the history of radiological physics, the search for an ideal body-cavity radiation dosimeter has been continuous. Many forms have been tried, but each has failed to fulfill one or more of the necessary or desirable characteristics. Even the gas-filled thimble-type ionization chamber in its standard form suffers from its large size, susceptibility to moisture, and the shadow-effect of the stem. These objections can be overcome by special design and construction, but such chambers are not available for routine use by the practicing radiotherapist. Even so, no other form of dosimeter has approached the general acceptance which has been accorded the thimble chamber. In extension of this search for the ideal dosimeter we have explored the quantitative response of certain substances which may be polymerized by high-energy radiation, with a view to their possible use for measuring dosage. It is of interest to note here that in certain respects the action of radiation on these substances is similar to ...