Tumor necrosis factor alpha (TNF-α) + epidermal growth factor (EGF) results in additive reduction in levels of aggrecan and type II collagen mRNA. Confluent monolayers of chondrocytes were treated for 24 hours with vehicle (CNTL), TNF-α (30 ng/ml), EGF (10 ng/ml) or TNF-α + EGF (n = 12). Levels of (a) aggrecan and (b) type II collagen mRNA were analyzed by northern blot of total RNA (10 μg). Changes in levels of (c) aggrecan and (d) type II collagen mRNA were quantified by densitometry. Levels were normalized to levels of 18S rRNA and data are expressed as the percentage of control ± standard error of the mean. a Significant difference from control (P < 0.001), b significant difference from TNF-α-treated and EGF-treated populations (P < 0.001).