Statins are most effective at inhibiting the viability of TNF-α-stimulated RA synovial fibroblasts. Synovial fibroblasts derived from patients with rheumatoid arthritis (RA) (n = 6) and osteoarthritis (OA; n = 6) were stimulated or not with 10 ng/ml tumor necrosis factor-α (TNF-α) for 24 hours before the addition of 3 or 10 μM atorvastatin or simvastatin. They were then maintained for a further 96 hours in the presence or absence of TNF-α and statin. XTT assays were performed on quadruplicate wells. The percentage cellular viability was determined by comparing statin-treated cultures with non-treated cultures in either the presence or absence of TNF-α as appropriate. Means and standard deviations are indicated by solid bars. *p < 0.05 for atorvastatin-treated versus simvastatin-treated RA fibroblasts. +p < 0.05 for RA versus OA TNF-α-stimulated fibroblasts.