Antitumor effect of our Candida utilis glucomannan preparation (YPS) was evaluated in two syngeneic transplantable tumors; the Lewis lung carcinoma (3LL) in C57BL/6 (B6) mice and the 3-methylcholanthrene (MCA)-induced fibrosarcoma in C3H/He mice. YPS inhibited preferentially the 3LL pulmonary metastases only when optimal dosage was given at an earlier stage; 7 daily intraperitoneal (i.p.) doses of 100 mg/kg per dose from the next day of tumor inoculation (1 X 10(5)/mouse, subcutaneously, s.c.) substantially reduced the number of metastatic nodules, yielding the inhibition ratio 54% on day 21. However, the same treatment delayed until day 8 markedly facilitated the metastatic spread (-105%). Postsurgical-adjuvant therapy with YPS (10 daily i.p. doses of 100 mg/kg per dose from the next day of surgery) was effective in improving the survival rate with no evidence of metastatic growth on day 200, even though the amputation of the tumor-bearing legs was performed after the pulmonary metastases had been established (on day 20). In the MCA-fibrosarcoma model, YPS treatment from day 3 (10 daily doses of 100 mg/kg per dose) was effective in prolonging the survival period. The 3LL local tumor was affected only marginally and temporarily, while the MCA-tumor was not at all.