Centbucridine, chemically known as 4-N-butylamino1,2,3,4-tetrahydroacridine hydrochloride, is a new quinoline derivative with local anesthetic action (synthesized at the Central Drug Research Institute, Lucknow, India). In animal experiments the drug is 5-8 times as active as lidocaine, being highly effective for infiltration anesthesia at a concentration of 0.5%. In mice, rats, and monkeys given graded doses of centbucridine (subcutaneously in rats and monkeys and intraperitoneally in mice), the LD50 was one-fourth that of lidocaine (1). Centbucridine does not cause local irritation on infiltration in animals (2). Preliminary studies (3-5) in human volunteers have confirmed its safety and effectiveness as a local anesthetic. We undertook the present study to compare the activity and safety of 0.5% centbucridine as an infiltration anesthetic with 2% lidocaine in a randomized double-blind noncrossover trial.