Objective: Tramadol hydrochloride is a centrally acting analgesic drug, used mainly as an analgesic for the treatment of moderate to severe pain. The local anaesthetic effect of tramadol in the rat sciatic nerves was demonstrated in our previous in vitro studies. In the present study, we investigated the effects of tramadol on the conduction of the compound action potentials (CAPs) in the rat sural and tibial nerves. Material and Methods: The effects of tramadol at concentrations of 0.1, 0.5 and 1.0 mM on CAPs in isolated rat sural and tibial nerves were examined with use of the modified sucrose-gap method, an extracelular recording technique, and with tonic (single) and phasic (100Hz) supramaximal stimulation. Results: Tramadol produced significant tonic and phasic conduction blocks in a concentration-and stimulation frequency-dependent manner in the sural and the tibial nerves. Tonic and phasic conduction blocks of the sural nerves were greater than that of the tibial nerves. At 0.1 and 1.0 mM tramadol concentrations, the phasic blocks in the rural and tibial nerves were measured as 14.3 +/- 2.5%, 66.5 +/- 4.6% and 11.4 +/- 0.8%, 39.1 +/- 1.6%, respectively. Tramadol extended the peak time and the half-falling time of CAPs obtained from the sural nerves, more than that obtained from the tibial nerves. Conclusions: The findings of this study showed that in the aural nerves, tramadol produces stronger tonic and phasic blocks, approximately twice more than the tibial nerves. The results may have the potential significance with regard to an improved understanding of possible peripheral effects of tramadol in patients taking for treatment of pain or local applications.