Chronothermodynamic recordings are useful in validating the efficacy of sympathetic blocks and sympathectomies. Guanethidine regional intravenous blocks at doses of 10, 20, or 30 mg without local anesthetic agents do not provide a sympathetic blockade. The technique can improve ongoing pain and dynamic mechanical hyperalgesia without necessarily involving the noradrenergic system. Mobilization pain and dynamic thermal hyperalgesia at warming up are not relieved by sympathetic blockades. Most cases of CRPS1 (algodystrophies) are sympathetically independent and can benefit from effective preventive analgesia, making intensive stress loading possible, with or without the use of dynamic splinting. Local guanethidine blocks can sometimes be effective on CRPS2 (causalgia), facilitating desensitization, and be followed by oral psychotropics for antalgic purposes. Therapies affecting the sympathetic system can have deleterious effects and indications for sympathectomies should remain exceptional, taking into account the natural evolution of such conditions, which is generally positive.