A new percutaneous approach to sympathectomy using radiofrequency denervation has seemed to offer longer duration and less incidence of postsympathetic neuralgia as compared to phenol sympathetic blocks. To compare these techniques, 17 patients underwent either phenol lumbar sympathetic blocks (n = 9) or radiofrequency denervation (n = 8). Duration of sympathetic block was followed by a sweat test and temperature measurements. Results indicate that 89% of patients in the phenol group showed signs of sympathetic blockade after 8 weeks, as compared to 12% in the radiofrequency group (P less than 0.05). Although the incidence of post sympathetic neuralgia appears to be less with radiofrequency denervation, further refinement of needle placement to ensure complete lesioning of the sympathetic chain will be required before the technique can offer advantages over current phenol techniques.