In this paper, we investigate network-aware mobile programs, programs that can use mobility as a tool to adapt to variations in network characteristics. We present infrastructural support for mobility and network monitoring and show how adaptalk, a Java-based mobile Internet chat application can take advantage of this support to dynamically place the chat server so as to minimize response time. Our conclusion was that on-line network monitoring and adaptive placement of shared data-structures can significantly improve performance of distributed applications on the Internet. (Also cross-referenced as UMIACS-TR-96-46)