Tumor necrosis factor alpha (TNF-α) enhances elongated cell morphology induced by epidermal growth factor (EGF). Confluent monolayers of chondrocytes were treated with vehicle, TNF-α (30 ng/ml), EGF (10 ng/ml) or TNF-α + EGF for 24 hours. (a) Cell morphology was observed by phase contrast microscopy. Arrowheads indicate spinous processes that appear following incubation with EGF or TNF-α + EGF. An elongated cell is defined as having a predominant axis with a length exceeding three times the maximum width of the cell. Digital images of live cultures were captured at 20 × objective magnification. Bar = 100 μm. Images shown are representative of three independent experiments. (b) The total number of elongated cells per field (1.376 mm2) were counted, averaged for at least three independent experiments (n = 3–5), and analyzed by analysis of variance. a Significant difference from control (P < 0.01), b significant difference from control (P < 0.001) and significant difference from EGF-treated cells (P < 0.01).