Four patients with ovarian cancer received 20 mg of sizofiran, a beta-1,3-glucan (molecular weight: 450,000), intramuscularly one day before and 4, 7, 11, 14, 18 and 21 days after second look laparotomy and recombinant interferon-gamma (rIFN-gamma) intraperitoneally on the day of second look laparotomy and 4, 7, 11, 14, 18 and 21 days thereafter. The peritoneal cavity was washed with physiological saline and peritoneal macrophages (M phi) were isolated. The number of M phi increased 30-1600 times during the treatment period. The concentrations of interleukin-1, interferon-gamma, tumor necrosis factor and prostaglandin E2 were also found increased in the supernatant fluid of M phi cultured for 24 hours with 10 micrograms/ml of lipopolysaccharide. The present study demonstrated that the activation of peritoneal M phi could be maintained and its number was increased by repeated dosing of sizofiran and rIFN-gamma in combination every three or four days in patients with ovarian cancer. Peritoneal M phi thus activated may exert an antitumor effect on ovarian cancer.