RPC has established itself as one of the more powerful communication paradigms for distributed computing. In recent years, object-oriented languages have impacted RPC semantics, with a number of variants providing remote method invocation and various forms of distributed object systems. At the same time, performance has changed little with the bottleneck being the network transport, in particular the in-kernel protocol implementations. This paper describes J-RPC, an RPC architecture that leverages user-level network interfaces (UNI) to circumvent the kernel on the critical path. It describes how the wire format and the RPC system can be engineered to allow zero-copy reception of Java objects and zero-copy transmission of arrays. All objects received are fully type-checked and can be directly used by the receiving program. The design is connection-oriented for performance and leverages the JVM's garbage collector when managing receive buffers. An implementation built from an off-the-shelf JVM and a commercial UNI is used to evaluate the architecture and the tradeoffs of type-safe, zero-copy data marshaling.