The effect of orally administered SSG, a beta-1,3-glucan obtained from the culture filtrate of the fungus Sclerotinia sclerotiorum IFO 9395, on the function of peritoneal macrophages in CDF1 mice was examined. Oral administration of SSG (20, 40, 80 or 160 mg/kg, daily for 10 consecutive days) enhanced the acid phosphatase activity of peritoneal macrophages. The greatest enhancing effect was observed at 80 mg/kg of SSG. Relatively long periods of administration (more than 10 consecutive days) were needed to induce significant enhancing effects. Phagocytic activity, candidacidal activity, hydrogen peroxide (H2O2) production and interleukin-1 (IL-1) production of peritoneal macrophages were also enhanced after the administration of SSG by the oral route (80 or 160 mg/kg). However, the durations of the activated state after completion of administration differed depending on the activity. Enhanced activity of lysosomal enzyme (acid phosphatase) was also shown in peritoneal macrophages taken from C3H/HeJ mice, which is a nonresponder strain to bacterial lipopolysaccharide (LPS). These results demonstrate that SSG given by the oral route can activate peritoneal macrophages in mice.