Previous findings showed that paclitaxel induces interleukin-8 (IL-8) transcription and secretion in ovarian cancer cells in vitro. We hypothesized that paclitaxel treatment, which is a standard care for ovarian cancer patients, may increase the secretion of IL-8, resulting in the elevated serum IL-8 levels. In this study, we investigated the relationship between paclitaxel exposure and IL-8 levels of an ovarian and a breast carcinoma cell line in vitro and serums of patients with ovarian carcinoma. Both MDAH 2774 ovarian and MCF-7 breast carcinoma cell lines were sensitive to paclitaxel-mediated cytotoxicity. However, supernatant levels of IL-8 assessed by enzyme-linked immunosorbent assay before and after treatment with different concentrations of paclitaxel were significantly lower in MCF-7 than in MDAH 2774. Serum IL-8 levels were measured in serum samples from patients with ovarian carcinoma before and after paclitaxel-containing treatment regimens. Forty-eight patients were included in the study. The basal level of IL-8 after paclitaxel-containing treatment was found to be significantly higher in the serums of patients who had high tumor burden than in patients who had optimal debulking surgery and low tumor burden. These data strongly suggest that IL-8 may be an important predictive marker for tumor volume as well as sensitivity to paclitaxel.