A human clinical study was undertaken to evaluate the effectiveness and safety of dexivacaine 2 per cent, mepivacaine 2 per cent, and mepivacaine 3 per cent. A double-blind technique was used to evaluate time of onset, duration, depth of anesthesia, and side effects. Results indicated no significant differences among the three anesthetics, except that mepivacaine 3 per cent had a significantly longer duration of soft-tissue symptoms in the mandibular block series. The few side effects noted were minimal and of no statistical significance. The evaluation of an anesthetic by the several parameters employed and especially by the over-all opinion of the anesthesia was deemed a valuable research method whem comparing the clinical effectiveness of local anesthetics.