OBJECTIVES: Identify local anesthetic activity of new derivatives of piperidine (LAS - local anesthetic substances) - LAS-202, LAS-203 and LAS-204 - for infiltration anesthesia. METHODS: The studies of infiltration anesthesia were conducted on guinea pigs by methods of Byulbring and Wade in 0,25% solutions, acute toxicity was investigated on white mice. Experimentally determined the strength of action and duration of anesthesia. RESULTS: Most local anesthetic activity noted in LAS-202, which power of action was equal to trimecaine, significantly exceeded lidocaine by 1.4 times, and novocaine by 1.3 times. The duration of complete anesthesia of LAS-202 is equal to trimecaine, and exceeds lidocaine and novocaine. Total duration of the local anesthetic effect of LAS-202 is significantly higher than trimecaine by 1.39 times, 1.79 times that of lidocaine, and 1.83 times that of novocaine. The index of anesthesia of LAS-203 and LAS-204 approaches the corresponding parameter of trimecaine. The complete skin insensitivity of guinea pigs in the administration of compounds is few shorter than that for trimecaine, equal to lidocaine, and longer than novocaine. The total duration of the LAS-203 is 1.06 times more than trimecaine, but LAS-204 more by 1.2 times. LAS-203 and LAS-204 exceeded the corresponding index of lidocaine by 1.3 times and 1.5 times, respectively, but exceeded novocaine by 1.4 times and 1.6 times, respectively. The LD50 of tested compounds are in the range of 425 mg / kg - 472.3 mg / kg. CONCLUSIONS: Of greatest interest is the compound LAS-202, which in force and duration of complete anesthesia is equal to trimecaine and exceeds lidocaine and novocaine. In general duration of action, it is superior to all the reference drugs and belongs to the low-toxic group of drugs. Therefore, LAS-202 is recommended for further studies.