✓ Rats bearing intracerebral 9L/Ro tumors were treated with 10 daily fractions of cesium-137 γ-rays, BCNU, or combinations of these two agents beginning on either Day 10 or Day 12 after implantation. The treatments were administered either 5 days/week for 2 weeks, with the weekend off, or 10 consecutive days. The median day of death for untreated tumor-bearing rats was Day 15, so Day 12 tumors can be considered late tumors and Day 10 tumors can be considered moderately early. Although all single- and multiple-agent treatments significantly (p < 0.05) increased the lifespan of tumor-bearing rats over that of the untreated controls, and all multiple-agent schedules significantly (p < 0.05) increased the lifespan over that of the single-agent therapies, none of the 10 consecutive day schedules increased the lifespan of tumorbearing rats significantly (p > 0.2) over that obtained with the 5-day/week schedules. Thus, the evidence from this tumor model suggests that no significant improvement in lifespan would be expected if malignant brain tumors were treated with radiation 7 days a week, either alone or in combination with chemotherapeutic agents such as BCNU.