The improvement in sensitive blockade induced by association of tramadol opioid injection was proved in animals and humans suggesting potencialization or synergism in effects. Nevertheless, there are no experiments concerning about the influence of codeine associated with local anesthetics (LA) injected simultaneously or previously to block sciatic functions (sensitive, motor and proprioceptive). Considering that codeine is readily available and costs much less than tramadol and similar opioids, it could be a strong candidate for an adjunct role in pain control. Objectives: The propose of this study was evaluate the influence of codeine analgesic opioid on duration of rat sciat nerve blockade induced by lidocaine using new pharmacological protocols. Methods: The functions of this mist nerve were analyzed comparing the effects of prior or associated injection of codeine. Fifthy (N=50) Wistar male rats were functional avaliated after they received differents injected drugs solutions in sciat nerve region: lidocaine and epinephrine (LA), local anesthetics with no vasoconstrictor (LA NV), codeine (COD), LA + codeine (LA + COD) or codeine 20 minutes prior to LA (COD 20'+ LA). The sensitive blockade was considered the absence of withdraw reflex after nociceptive and pressoric stimulous (analgesimether and forceps), the motor was evaluated the duration of claudication and proprioceptive by de absence of hopping and tactile response (score 0-3). Results : The blockade duration of (LA + COD) was greater than (COD) and than (COD 20' + LA) and than other groups (p<0.05). Conclusions : The results suggest synergism between codeine and LA improving the efficacy of blockade which could lead to a new perspective in dentistry pain control.