Background: Pseudomyxoma Peritonei (PMP), a peritoneal mucinous neoplasm of appendix origin, is associated with inflammation and fibrosis which is central to the disease biology. Here, we examine possible biomarkers or regulators of PMP biology in peritoneal tumor microenvironment and in serum. Methods: Ascites, peritoneal washings and serum were collected from PMP patients. Cytokines and C-reactive protein (CRP) levels were determined using Milliplex immunoassays. Immunohistochemistry (IHC) was performed on formalin-fixed tissue sections. Statistical analysis was performed by the Mann Whitney U test and Bivariate analysis. Results: Serum CRP was significantly elevated in PMP patients (n=29) versus controls (n=4) (0.124 vs 0.004 mg/dl, p = 0.003). CRP levels were lower in ascites (0.028 vs 0.124 mg/dl, p = 0.014), but correlated with serum levels (R = 0.65, p < 0.001). Cytokines typically elevated after infection or injury—TNF-α, IL-1α, IL-1β and γ INF—were not significantly elevated in PMP ascites; however, IL-6, IL-8, IP-10 and MCP-1 were consistently higher (p < 0.001) in PMP with ascites (n=29) when compared to control peritoneal washings (n=9). Both serum and ascites from 10 patients were evaluated for these four cytokines. Ascites levels were significantly elevated compared to their respective serum for IL-6 (1107 vs 3.18 pg/ml, p < 0.001), IL-8 (167 vs 1.59 pg/ml, p < 0.001), IP-10 (5454 vs 504 pg/ml, p < 0.001) and MCP-1 (2420 vs 234 pg/ml, p = 0.002) but the serum levels were not significantly elevated compared to controls (n=6) (p = 0.31, 0.2, 0.63, 0.37 respectively). IHC revealed staining for IL-6 and IL-8 in stromal cells and focal staining of tumor for IP-10 and MCP-1. Recombinant IL-6-treated LS174T cells (mucinous colon cancer cell line) showed increased proliferation (p<0.009) which was inhibited by anti-IL-6 antibodies (p<0.004). Conclusions: CRP, a liver-synthesized marker of systemic inflammation, is elevated in PMP, and may have clinical utility. The results support local synthesis for cytokines IL-6, IL-8, IP-10 and MCP-1 in the peritoneum. Interestingly, the pattern of cytokines appears to be distinct from those following injury or infection. Further studies may yield novel targets for future treatment.