To study the role of TNFa in articular nociception, afferent nerve fibers with a receptive field in the acutely inflamed knee joint were recorded extracellularly in sodium thiopentone-anesthetized adult rats. The inflammation was induced by an intraarticular injection of 0.1 ml kaolin, followed by an injection of 0.1 ml carrageenan. Seven hours after induction of inflammation, the knee joint was mechanically stimulated by innocuous (20 mNm) or noxious (40 mNm) torque for 15 sec each. Fibers were classified as A[delta]- or as C-fibers by their conduction velocity. Initially the investigated C-fibers responded with 58.3±8.2 action potentials to innocuous and with 244.4±46.5 action potentials to noxious test stimuli. The intraarticular injection of Tyrode did not affect the response rate, whereas an intraarticular injection of 100 ng Etanercept decreased the response rate of C-type fibers to innocuous torque by 29 % and to noxious stimulation by 43 % beginning 30 min after injection. The effect lasted more than 1 hour. Responses of A[delta]-fibers to innocuous stimuli were nearly unchanged, but increased up to 121 % after noxious stimulation. Our data indicate that blockade of TNFa decreases the mechanosensitivity of articular C-fibers but not of articular A[delta]- fibers in the acutely inflamed knee joint.