This paper presents JavaSplit, a portable runtime for distributed execution of multithreaded Java programs. Java-Split transparently distributes threads and objects of an application among the participating nodes. Thus, it gains augmented computational power and increased memory capacity without modifying the Java multithreaded programming conventions. Java-Split works by rewriting the bytecodes of a given parallel application, transforming it into a distributed application that incorporates all the runtime logic. Each runtime node carries out its part of the resulting distributed computation using nothing but its local standard (unmodified) Java Virtual Machine (JVM). This is unlike previous Java-based distributed runtime systems, which use a specialized JVM or utilize unconventional programming constructs. Since Java-Split is orthogonal to the implementation of a local JVM, it achieves portability across any existing platform and allows each node to locally optimize the performance of its JVM, e.g., via a just-in-time compiler (JIT).