The survival-enhancing capabilities of particulate (P) and soluble (F) glucan, a B-1,3 polyglycan biological response modifier, were assayed in 60Co irradiated mice. Although glucan-P was slightly more effective than glucan-F, both glucans significantly enhanced survival in otherwise lethally irradiated (9.0-11.0 Gy) C3H/HeN mice. Following 9.0 Gy, 60% of the glucan-P treated and 53% of the glucan-F treated mice exhibited long-term survival as opposed to 0% of the radiation control mice. The survival-enhancing effects of glucan-P and glucan-F decreased as the radiation dose increased to 11.0 Gy. At higher radiation doses (e.g., 12.0 Gy) neither glucan preparation was capable of enhancing survival. Both glucan-P and glucan-F enhanced the recovery of peripheral blood white cell numbers, platelet numbers, and hematocrit values. In addition, both agents increased endogenous pluripotent hemopoietic stem cell numbers in sublethally irradiated mice. Taken together, these results demonstrate that both glucan-P and glucan-F can significantly enhance survival in lethally irradiated mice. However, these agents appear to function specifically by enhancing hemopoietic recovery and are not effective at radiation does also known to induce gastrointestinal damage.