The Ethernet communications network is a broadcast, multiaccess system for local computer networking, using the techniques of carrier sense and collision detection . Recently we have measured the actual performance and error characteristics of an existing Ethernet installation which provides communications services to over 120 directly connected hosts. This paper is a report on some of those measurements—characterizing “typical” traffic characteristics in this environment and demonstrating that the system works very well. About 300 million bytes traverse the network daily; under normal load, latency and error rates are extremely low and there are very few collisions. Under extremely heavy load—artificially generated—the system shows stable behavior, and channel utilization approaches 98 percent, as predicted.