['To analyse the gene expression of tumour necrosis factor-alpha (TNF-alpha) in human dental pulps, under normal and inflammatory conditions and to examine the association between any observed alterations in the expression of this cytokine with the severity of the clinical symptoms.', 'Eighteen pulpal samples were obtained from single-rooted human teeth. Six of the teeth were normal (group A), six had been diagnosed with reversible pulpitis (group B), and the remaining six were from teeth diagnosed with irreversible pulpitis (group C). TNF-alpha gene expression was semi-quantitatively analysed in each sample with RT-PCR, and the results from each group of teeth were compared with the Kruskal-Wallis and Mann-Whitney tests.', 'Tumour necrosis factor-alpha was detected in all three groups of dental pulp. Statistical analysis provided evidence of a significant increase of TNF-alpha gene expression associated with irreversible inflammation compared with healthy controls (P = 0.002). No such difference was detected in reversibly inflamed pulp in comparison to healthy teeth (P = 0.699).'] Is irreversible but not reversible pulpitis associated with up-regulation of tumour necrosis factor-alpha gene expression in human pulp?