In order to deliver a high concentration of CDDP in tumor tissue, we attempted to infuse CDDP intra-arterially for preoperative patients with resectable gastric cancer. Thirty-two patients (21 males and 11 females) were treated. The concentration of platinum was measured in cancer tissue, normal mucosa, lymph nodes without metastasis at the greater curvature. These were gathered operatively and in serum just before operation. The serum concentration of free-CDDP was also measured. Student's-t test was performed with the data. After intra-arterial injection of 60 mg CDDP, the mean concentration of platinum in cancer tissue was 1.11 +/- 0.45 microgram/g and after intravenous injection of 40 mg CDDP that was 0.30 +/- 0.11 microgram/g. After intra-arterial injection of 40 mg CDDP, the mean concentration of platinum in cancer tissue was 0.64 +/- 0.12 microgram/g, which was significantly higher than in normal gastric mucosa (0.27 +/- 0.06 micrograms/g) or serum (0.37 +/- 0.10 micrograms/ml) (p less than 0.025). The mean concentration of platinum in cancer tissue was higher than in the lymph nodes (0.45 +/- 0.10 micrograms/g), but there was no significant difference. In sera the concentrations of free-CDDP were all under the detectable limit. It was concluded that intra-arterial injection therapy of CDDP was an effective method to maintain a high concentration of CDDP in gastric cancer tissue.