[en] This thesis is concerned with the effect of crocetin on the radiosensitivity of cancer. It is also concerned with a study of the mechanism of action of crocetin, which presumably increases radiosensitivity by increasing oxygen diffusivity. In vivo studies were conducted using a Walker-256 carcinoma grown in the thigh muscles of male Sprague-Dawley rats. The minimum dose of X-rays necessary to induce cancer regression was first determined. It was then found that lower dosages of irradiation would also cure the tumors provided crocetin was also given to the animals. Further, it was found that there is an optimum crocetin concentration which is most effective in inducing the cure, as well as an optimum scheduling of the dosages. The data were found to be statistically significant, and crocetin was found to be most effective in the salt form when given on the day before, and immediately after, irradiation. In vitro studies were made using cell cultures of both normal and cancerous rat muscle cells. This was done to determine whether or not crocetin acts on a purely cellular level in the animal or on a systemic level. The first tests showed that crocetin increased cell growth rates, for both normal and cancer cells. Then a similar approach to the in vivo work was adopted for utilizing both radiation and crocetin with the cultures. It was found that the crocetin concentration which induced maximum growth of the tumor cells caused the cells to also be more radiosensitive. Thus it would appear that the beneficial effects of crocetin are due to an interaction on the cellular level, presumably by causing increased growth due to increased oxygen transport