['To determine whether a Bcl-x(S) adenoviral vector has therapeutic potential in an ascites model of human breast cancer in nude mice.', 'Advanced ascites were developed by injecting mice intraperitoneally (IP) with MDA-MB-231 human breast carcinoma cells. Mice received sequential IP injections of the Bcl-x(S) virus or a control lac-Z adenovirus. A third group of mice received no virus. Tumor burden and survival were monitored. Histopathology and necropsies were performed on mice.', 'A single injection of the Bcl-x(S) adenovirus produced no systemic or local toxicity and no abnormal histopathology in normal mice. However, abdominal organs within these mice were transduced with the Bcl-x(S) vector. Adenoviral gene transduction efficiency in MDA-MB-231 ascites was 36+/-6.40% (n = 3). Percent weight change differences revealed that ascites bearing mice injected three times with the Bcl-x(S) vector showed a statistically significant decrease in tumor burden compared with lac-Z-injected mice (n = 7; P = .012 on days 10-15 after the first injection). Mice injected with the Bcl-x(S) vector had significantly greater survival relative to lac-Z-injected mice (n = 7; P = .0004). Bcl-x(S) protein expression was detected in aspirates of mice injected with the Bcl-x(S) vector but not the lac-Z vector. Necropsies revealed that ascites bearing mice injected with Bcl-x(S) vector lacked carcinoma in the peritoneal cavity compared with control mice.'] Does a bcl-x ( S ) adenovirus demonstrate therapeutic efficacy in an ascites model of human breast cancer?