Pretreatment with two distinct antitumor substances extracted from pine cone of Pinus parviflora Sieb. et Zucc. protected mice from the lethal effects of E. coli infection. Intraperitoneal administration of these fractions transiently induced differentiation-inducing factor (DIF) with a peak at 1-2hr. The rapid decay of DIF activity from the peritoneal cavity was followed by polymorphonuclear cell (PMN) accumulation and enhancement of superoxide generation (assayed with luminol-dependent chemiluminescence (LDCL] by peritoneal exudate cells. The superoxide generation by adherent cells was similarly enhanced by pretreatment, but was only 10-20% of that of the peritoneal exudate cells. Fractions that showed comparable antitumor/antimicrobial activity were also obtained from seed shells and cones of other pine trees of Japanese and foreign origin. On the other hand, a neutral polysaccharide fraction from Pinus parviflora Sieb. et Zucc. that lacked any of these activities did not induce PMN accumulation, DIF activity or LDCL generation. The results suggest a significant role in PMN activation for the expression of antimicrobial activity induced by pine cone extracts.