Oncolytic virus H101 is an adenovirus with an E1B-55KD gene deletion, which selectively replicates in tumor cells, rather than in normal cells, resulting in specific tumor cytolysis. Taking the selective killing of peritoneally planted tumor cells by the oncolytic virus H101 as the rationale for the ascites treatment, we report in this paper the intraperitoneal H101 in 9 patients with malignant ascites. The interval between the paracentesises increased from a mean of 12.4+/- 3.4 to 39.9 +/- 11.6 days (p < 0.001). The 30-day response was classified into complete response (CR) (no fluid recurrence), partial response (PR) (fluid recurrence <50%), and no response (NR) (fluid recurrence > or =50% or requiring paracentesis). Nine (9) patients had 3 CRs, 2 PRs, and 4 NRs. Intraperitoneal H101 was well tolerated, and no severe adverse effects were observed. Further, this report also highlights the potential of H101 in malignant ascites treatment.