AIM: To examine the paclitaxel concentrations in plasma and ascites after its intravenous administration in patients with ascites due to peritonitis carcinomatosa resulting from advanced gastric cancer. METHODS: Two patients with ascites due to peritonitis carcinomatosa resulting from gastric cancer were included in this study. The paclitaxel concentrations in plasma and ascites were investigated for 72 h in case 1 and 168 h in case 2 after intravenous administration. RESULTS: The paclitaxel concentration in plasma peaked immediately after administration, followed by rapid decrease below the threshold value of 0.1μmol (85 ng/mL) within 24 h. In contrast, the paclitaxel concentration in ascites increased gradually for 24 h after administration to a level consistent with the level found in plasma. After 24 h the level of paclitaxel in ascites and plasma became similar, with the optimal level being maintained up to 72 h following administration. CONCLUSION: The concentration of paclitaxel in ascites is maintained within the optimal level for the treatment of cancer cells for up to 72 h after intravenous administration. Paclitaxel is a promising drug for the treatment of malignant ascites of gastric cancer. AIM: To examine the paclitaxel concentrations in plasma and ascites after its intravenous administration in patients with ascites due to peritonitis carcinomatosa resulting from advanced gastric cancer. METHODS: Two patients with ascites due to peritonitis carcinomatosa resulting from gastric cancer were included in this study. The paclitaxel concentrations in plasma and ascites were investigated for 72 h in case 1 and 168 h in case 2 after intravenous administration. RESULTS: The paclitaxel concentration in plasma peak immediately immediately after administration, followed by rapid decrease below the threshold value of 0.1 μmol (85 ng / mL) within 24 h. In contrast, the paclitaxel concentration in ascites increased gradually for 24 h after administration to a level consistent with the level found in plasma. After 24 h the level of paclitaxel in ascites and plasma became similar, with the optimal level being maintained up to 72 h following administration. CONCLUSION: The concentration of paclitaxe l in ascites is maintained within the optimal level for the treatment of cancer cells for up to 72 h after intravenous administration. Paclitaxel is a promising drug for the treatment of malignant ascites of gastric cancer.