Despite the fact that the anticholinesterases, mainly neostigmine, has been used for many years to antagonize a nondepolarizing neuromuscular blockade, until recently nothing was known about their pharmacokinetics and dynamics in anesthetized patients. This deficiency was largely due to lack of a suitable analytic technique to measure the concentration of these drugs in body fluids, most importantly serum. Recently it was developed a method by which the serum concentrations of neostigmine, pyridostigmine, edrophonium and their metabolites can be measured. Recently, pyridostigmine and edrophonium have gained popularity to use for reversing a nondepolarizing muscle relaxants. We have studied newly introduced vecuronium effects and its reversal with pyridostigmine. The results were as follows; 1) Spontaneous recovery index by vecuronium 0.1 mg/kg was 620.8 sec. 2) Recovery index by the pyridostigmine 160 ㎍/kgreversal was significantly shortened as 134.0 sec in vecuronium 0.1 mg/kg block. 3) Tetanic stimulation (100 Hz, 5 sec) was sustained after 75% recovery of twitch heitht by pyridostigmine 160 ㎍/kg reversal.