The term refinement algebra refers to a set of abstract algebras, similar to Kleene algebra with tests, that are suitable for reasoning about programs in a total-correctness framework. Abstract algebraic reasoning also works well when probabilistic programs are concerned, and a general refinement algebra that is suitable for such programs has been defined previously. That refinement algebra does not contain features that are specific to probabilistic programs. For instance, it does not include a probabilistic choice operator, or probabilistic assertions and guards (tests), which may be used to represent correctness properties for probabilistic programs. In this paper we investigate how these features may be included in a refinement algebra. That is, we propose a new refinement algebra in which probabilistic choice, and probabilistic guards and assertions may be expressed. Two operators for modelling probabilistic enabledness and termination are also introduced.