Our objectives are (1) to compare tumor induction by X-irradiation, by simulated chemotherapeutic regimens of L-phenylalanine mustard (L-PAM) or 5-Fluorouracil (5-FU) and by combined modalities and (2) to learn more about the properties of the tumors induced and the mechanisms involved. The female Sprague-Dawley rat that is genetically predisposed to the development of mammary tumors is used as the test animal with treatments beginning when the rat is about 50 days old. We X-irradiated the whole abdomen (both halves, 2/2) with a single dose of 100, 200, or 400 rads or 2 doses of 200 rads each with an interval of four weeks between doses. We irradiated 1/2 of the abdomen of other rats with the same doses plus a dose of 800 rads for some. We have given other rats 0.25x, 0.5x, 1.0x or 2.0x a "standard" dose of 12 mg 5-FU/kg body weight administered intraperitoneally on days 1, 2, 3, 4, 6, 8, 10, and 12 of the treatment regimen. We have given other rats 0.25x, 0.5x, 1.0x, or 2.0x a "standard" dose of 0.3 mg L-PAM/kg body weight/day fed by stomach tube for 5 days, waited four weeks, and then repeated the doses. We have also given various combinations of X-rays and one or the other of the drugs. We will treat more rats to increase our sample sizes and test other permutations in the time of X-ray and L-PAM treatments. Tumors are excised as they develop to determine their type and to assay superoxide dismutase levels and some receptor sites of the tumors. We also monitor the weights of the rats after treatments and do periodic blood counts looking for hematopoietic changes.