Glucan, a (beta)1,3 linked glucopyranose isolated from Saccharomyces cerevisiae, has been demonstrated to have profound stimulatory effects on the reticuloendothelial and immune system following systemic administration. Additionally, glucan has been shown to be effective in modifying the course of experimentally induced neoplastic disease states. The current study was undertaken to evaluate the effect of glucan on experimentally induced infectious disease states. Since infection in the immune compromised host has become an increasingly frequent problem, additional studies were undertaken to examine the effect of glucan on experimental animals which were immune suppressed by neoplasia or chemotherapy Glucan was observed to significantly increase survival in normal mice with systemic Staphylococcus aureus septicemia. Histological examination of the kidneys revealed that glucan significantly inhibited renal necrosis associated with systemic staphylococcal disease. Further studies indicated that glucan administration not only enhanced survival of mice with lymphocytic leukemia, but also increased survival of leukemic mice with experimentally induced staphylococcal septicemia Glucan was also observed to significantly improve survival in mice which were immunosuppressed with the chemotherapeutic agent cyclophosphamide and then challenged with Staphylococcus aureus. Glucan, as a single pre-treatment regimen, resulted in a median survival time (MST) of 12.5 days, as compared to 7.5 days in the control group. A 1.4 day MST was observed in mice pre-treated with cyclophosphamide and subsequently challenged with S. aureus. However, when glucan and cyclophosphamide were administered together, a MST of 9.0 days was observed In contrast to the significant (p < 0.05) decrease in peripheral leukocytes counts observed in the cyclophosphamide-treated mice, the administration of glucan resulted in maintenance of peripheral leukocyte numbers. Additionally, the profound renal necrosis observed in mice pre-treated with cyclophosphamide was ameliorated by conjoint glucan administration. (Abstract shortened with permission of author.)