The Massachusetts General Hospital Laboratory of Computer Science created a library of computer-aided-instruction (CAI) programs in 1972. An experimental network of Cai programs, made possible by National Library of Medicine (NLM) support, was set up in July 1972, operating over commercial communication lines. Programs developed by Massachusetts General, Ohio State University and the University of Illinois Medical College were made available to users with terminals in about 36 cities through a local telephone number. During the first two years of the program over 80 institutions participated. A trial of the Massachusetts General programs, in conjunction with the Continuing Education Committee of the American College of Emergency Physicians, was conducted in five representative community hospitals. The hospitals put up the cost of the terminals and the telephone charges. Results of the study showed that 12 of the 40 (30%) emergency physicians in the target population took 10 or more programs. They gave the programs a favorable overall rating--1.6 on a scale of 1 (strongly positive) to 5 (strongly negative).