Cytokines may be pathophysiologically involved in hyperalgesia. Uncertainty exists about the types of cytokines and their site of action. To study the role of key pro- and anti-inflammatory cytokines in a chronic constriction model of neuropathic pain, mRNA expression of TNF, IL-1β, IL-6, and IL-10 was quantified using competitive RT-PCR. Each cytokine mRNA in rat sciatic nerve was examined at days 3, 7, 14, and 45 after chronic constriction injury (CCI). We also undertook behavioral testing of these rats. Thermal warming and touch thresholds were significantly reduced at days 3, 7, and 14 in the CCI group, compared with the sham-operated group. Cytokine gene expression in sciatic nerve was significantly increased at day 7 for IL-1β and IL-6 and at day 14 for TNF. Expression of IL-10 underwent a gradual and progressive increase, reaching statistical significance at day 45.