Quantitative Sensory Testing (QST) is a psycho-physiological test used to identify dysfunction of individual nerve fiber types. In the present study, we investigated whether selective nerve fiber dysfunction, as assessed by QST, correlates with the effectiveness of epidural steroid injections (ESI) in patients with lumbar radiculopathy. Twenty patients with unilateral painful sciatica caused by disc herniation participated in this open study. Before ESI, quantitative thermal and mechanical sensory testing was conducted at the most painful dermatome and the contralateral dermatome. The primary outcome measure used was the self-recording of pain intensity twice daily with a 0-10 numerical pain scale (NPS). Secondary efficacy measures included the Short Form of the McGill Pain Questionnaire, the straight leg raising test, and the lumbar range of motion. A significant difference in all types of sensory thresholds between the affected and the contralateral dermatomes was detected at baseline. All outcome measures improved subsequent to the ESI. A significant positive correlation was found between the increase in cold sensation thresholds of the affected dermatome (Adelta-fiber dysfunction) and the improvement in NPS. The increase in touch and vibration thresholds (Abeta-fiber dysfunction) was found to be inversely correlated with the improvement in NPS. No correlation was found between heat sensation thresholds (C fibers) and any of the outcome measures. These results suggest that QST has the potential to be an important tool in the selection of the appropriate treatment (e.g., ESI versus surgery) for patients with sciatica and may assist in identifying the mechanisms of pain generation in these patients.