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 metabolities can be measured. Recently,k 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 0.1mg/kg was 620.8 sec. 2) Recovery index by the pyridostigmine 160ug/kg reversal was significantly shortened as 134.0sec in vecuronium 0.1mg/kg block. 3) Tetanic stimulation (100Hz, 5sec) was sustained after 75% recovery of twitch height by pyridostigmine 160ug/kg reversal.