Abstract: Parametric, semiparametric and nonparametric tests have been used to com- pare two samples of censored survival times possibly in the presence of covariates. The power functions of these tests are compared by Monte Carlo simulations under certain misspecifications commonly found in real problems. The nonparametric test (logrank) is in general less powerful than the parametric and semiparametric (score) tests. The performance of these latter tests are equivalent Ver menos