Background: Recent evidence implicates the inflammatory cytokine tumor necrosis factor as a major cause of radiculopathy. Yet, whereas open-label studies with systemically delivered tumor necrosis factor inhibitors have yielded positive results, a placebo-controlled study failed to demonstrate efficacy. One variable that may have contributed to poor outcomes is low drug levels at the site of nerve inflammation. To date, no studies have evaluated the efficacy or safety of epidurally administered anti–tumor necrosis factor agents. Methods: A double-blind, placebo-controlled, dose-response study was conducted to evaluate an epidural tumor necrosis factor inhibitor. Twenty-four patients with subacute lumbosacral radiculopathy were randomly assigned to receive two transforaminal epidural injections of 2, 4, or 6 mg of entanercept 2 weeks apart in successive groups of eight. In each group, two patients received epidural saline. A parallel epidural canine safety study was conducted using the same injection doses and paradigm as in the clinical study. Results: The animal and human safety studies revealed no behavioral, neurologic, or histologic evidence of drug-related toxicity. In the clinical arm, significant improvements in leg and back pain were collectively noted for the etanercept-treated patients, but not for the saline group, one month after treatment. One patient in the saline group (17%), six patients in the 2-mg group (100%), and four patients each in the 4-mg and 6-mg groups (67%) reported at least 50% reduction in leg pain and a positive global perceived effect one month after treatment. Six months after treatment, the beneficial effects persisted in all but one patient. Conclusion: Epidural entanercept holds promise as a treatment for lumbosacral radiculopathy.