In programming semantics, monads are used to provide a generic encapsulation of side-effects. We introduce a monad-based metalanguage that extends Moggi’s computational metalanguage with native exceptions and iteration, interpreted over monads supporting a dcpo structure. We present a Hoare calculus with abnormal postconditions for this metalanguage and prove relative completeness using weakest liberal preconditions, extending earlier work on the exception-free case.