aThe effects of lidocaine on the action potential of crushed sciatic nerves were investigated. The sciatic nerves of the rats were removed 5, 15, 25, and 38 days after the crushing and the compound action potentials were recorded with sucrose gap technique. The nerves were treated with 1 mM lidocaine and the conduction blocks of nonfrequency dependent block (NFDB) and frequency depended block (FDB) at 10, 40, and 100 Hz were determined. In intact nerves, the NFDB effect of lidocaine was 38.4 +/- 0.7 %. On the 15th day after the crush, the NFDB was increased to 60.1 +/- 1.3%. On the 38th day NFDB was decreased to 46.0 +/- 0.8%. The following days after the crushing, lidocaine caused a very high rate of FDB with 10, 40, and 100 Hz stimulation. The high NFDB ratios approached normal levels with the improvement of regeneration, but FDB ratios continued to stay at high levels. The results showed that the ratios of FDB and NFDB were increased on the crushed nerve. It was concluded that, in the regeneration conditions of crushed rat sciatic nerves, the sensitivity to local anesthetic increases more than in intact nerves.