Remote Method Invocation is one of the most popular communication paradigms in distributed computing. However, its synchronous nature may affect application performance. Asynchronous, or non-blocking, RMI addresses the issue by implicitly introducing concurrency into an application and allowing it to interleave computations with communications. In this paper, we analyze certain semantic issues raised by asynchronous RMI, such as execution order, exception handling, cancellation, data consistency, and more. Solutions are proposed, and a realization of asynchronous RMI within our multi-protocol, extensible communication framework for Java (termed RMIX), is presented.