Concentrations of HCFU and 5-FU in blood and tissues of resected specimens were evaluated in 28 patients with ovarian tumor (pathologically benign 10, malignant 18) preoperatively considered to be malignant. 1) No significant difference of HCFU and 5-FU concentrations in sera, uterus and peritoneum was observed between the benign and cancer groups. 2) No significant difference of HCFU concentration in tissues of ovarian tumor was recognized between the benign and malignant groups, but as for 5-FU concentrations, 0.116 +/- 0.198 micrograms/g tissue in the cancer group was considerably higher than 0.021 +/- 0.144 micrograms/g tissue in the benign group (p = 0.085). Furthermore, the 5-FU level in ovarian cancer tissues was much higher than that in the tissues of the contralateral normal ovary, suggesting that degradation of 5-FU might be delayed in cancer tissue. 3) HCFU concentration in omental tissues from cancer patients was 0.043 +/- 0.061 micrograms/g tissue, significantly higher than that from benign patients, 0.004 +/- 0.008 micrograms/g tissue (p = 0.024). As for 5-FU concentration, no apparent difference was found, suggesting that 5-FU might be quickly eluted or metabolized in omental tissue.