The pro-inflammatory cytokine, tumour necrosis factor-α, TNF-α, is dysregulated in malignant compared with normal ovarian surface epithelium (OSE). Several epidemiological studies have associated inflammation with ovarian tumorigenesis, with TNF-α playing a key role in modulating invasion, angiogenesis and metastasis. Here, we show that TNF-α also induces expression of arate-limiting enzyme in arginine synthesis, argininosuccinate synthetase (AS), thereby linking inflammation with several arginine-dependent metabolic pathways, implicated in accelerated carcinogenesis and tumour progression. Having identified AS mRNA induction in TNF-α-treated IGROV-1 ovarian cancer cells, using RNA-arbitrarily primed-PCR, we then observed differential regulation of AS mRNA and protein in malignant, compared with normal, OSE cells. A cDNA cancer profiling array with matched normal ovarian and ovarian tumour samples revealed increased expression of AS mRNA in the latter. Moreover, AS protein co-localised with TNF-α in ovarian cancer cells, with significantly higher levels of AS in malignant compared with normal ovarian tissue. Increased co-expression of AS and TNF-α mRNA was also observed in 2 other epithelial tumours, non-small cell lung and stomach cancer, compared with normal corresponding tissues. In summary, high levels of AS expression, which may be required for several arginine-dependent processes in cancer, including the production of nitric oxide, proline, pyrimidines and polyamines, is regulated by TNF-α and may provide an important molecular pathway linking inflammation and metabolism to ovarian tumorigenesis. © 2007 Wiley-Liss, Inc.