BACKGROUND: This study is to demonstrate that the estimates of effective concentration (EC) inferred by logit, probit, and sigmoid Emax can be declared to be similar. METHODS: The estimates of EC (5, 25, 50, 75, 95 [%]) of 24 vecuronium concentration-single twitch response data were obtained with three pharmacodynamic methods. A paired t-test with Bonferroni's correction was used. RESULTS: The distribution of estimates by probit were narrower than that of those by logit and sigmoid Emax. The estimates of logit and sigmoid Emax were closely similar. CONCLUSIONS: It suggests that the EC estimates of other paper analysed by the different pharmacodynamic method could be lower or higher.